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I don't know what would be the best action, but at least you probably can't change anything regarding your existing ticket until the flight(s) are cancelled. SAS pilots' strike obviously affects only SAS flights (and not necessarily even all of those, since some flights are operated by separate subsidiaries and partner airlines and their pilots are not on strike), so if you fly other airlines then the strike should not be a problem. However, many other airlines have had various other problems lately that has lead into significant delays and cancellations, which may lead into misconnects if your itinerary includes changing planes somewhere.

Actually I think nearly all of the larger airports especially in Europe have recently had this sort of trouble. The main reason being staff shortage: during the worst days of pandemic when travel was more or less halted, the airport operators (and related companies) dismissed significant portion of their work force and now they are struggling to recruit enough people.

Actually, I think the charge is based on kilometres. 😉 In most of Europe (British isles might be the exception), you rarely encounter anything measured in miles.

Found an article describing the best places to see puffins in Iceland and I think that Akurey in front of Reykjavík might be the only spot that might be near any cruise ship route, although still at least few hundred meters away.

Never been in Munich myself, but I presume H gates are for flights from/to non-Schengen countries (like USA), while G and K are gates for intra-Schengen area flights. And passport control will occur when you move from non-Schengen side to Schengen side of the airport (or vice versa). And remember that if it is airlines that mess up your flight schedule, they have to arrange you new transportation to your destination if the original connection does not work. And given that both Lufthansa and SAS offer several flights between Munich and Stockholm, you will most likely accomodated on a later flight if your flight to Munich arrives significantly late. And if there is a delay you may be eligible for compensation or at least for duty of care (food, communitions, possibly accomodation if there is need to wait overnight). The magic word here is EC261. But if your first flight arrives on time (or possibly even bit early), you don't have to worry about these things.

Military museum in Suomenlinna offers information about Finnish military history and that certainly includes Winter war (and the related Continuation war). The sea fortress Suomenlinna is worth a visit even if one does not visit the museums there. However, worth a note that since most people have Saturdays off from work, that might lure also quite many locals there, although perhaps not into museums.

That name didn't ring a bell for me outright, but after little googling I learned what she has done and apparently she designed some items for Arabia, which means that Iittala & Arabia Design Centre and its Design Museum Arabia might have some, but I cannot be absolutely sure about that. At least there is ceramic and glass items designed by many well-known Finnish designers.

There is no true old town in Helsinki, at least in same sense as there is in Stockholm and Tallinn for example. There is city district called Vanhakaupunki (Old Town) on the west side of the mouth of river Vantaa where Helsinki was originally founded in 1550. In its current form, there is barely any signs of history from those early days of Helsinki. The city was later moved further south into the area where there is the current city centre, although for long Helsinki was tiny city and only started to grow in late 18th century and the majority of the buildings in central Helsinki date from 19th century or later. Since I reside in Helsinki, I have only vague ideas on what sort of tours the cruise companies offer, but if you prefer to wander around by yourself rather than go with a tour group, it is quite viable choice to skip tours. There is quite extensive network of public transportation (see HSL website for more information) and nearly all people understand English, although some random persons stopped on a street might be slightly hesitant with their foreign language skills.

Both of these waterparks are near metro stations, although from the city centre Keilaniemi is closer and it is slightly easier to travel there as you can pick any westbound metro train, whereas to go to Rastila you must ensure that the eastbound train heads to Vuosaari rather than Mellunmäki, which is the terminus for every other eastbound train.

Suomenlinna is certainly a good option, bring a flash light and you can explore the dark corridors within fortress walls. Classic sights for kids in Helsinki are of course amusement park Linnanmäki and Korkeasaari zoo, for the latter there is possibility to take a boat from the Market Square. But I guess these are not that superspecial compared to other amusement parks or zoos elsewhere. Now, if climbing interests you, Adventure park(s) Korkee might be good choice as it offers adventure courses on trees. There are two locations of these parks, Mustikkamaa might be more child friendly choice and it is located on the island next to Korkeasaari, so it could be possible to combine the two. Other location is at Paloheinä in northern Helsinki and there is only a treetop course that accepts customers that are 110 cm or longer. Sadly the website of Korkee appears to be only in Finnish, but the images there at least give some idea what sort of activity these parks offer. If it is warm (or even hot) weather, I guess water activities would be perfect choice to spend some time. For more than just basic swimming next to a beach there are few waterparks in Helsinki region: Laguuni and especially its Keilaniemi (Keilis) venue in Espoo might offer most, although they have some activity also next to the beach at Hietaniemi (Hietsu). Another floating water park is located at Rastila beach in eastern Helsinki, sadly Lappis water parks has only Finnish language website at the moment. Then there is also the classic waterpark Serena in Espoo, but the location is somewhat remote. And Flamingo spa waterpark in Vantaa offers also water activities, but it is entirely indoor facility. If you don't necessarily want fancy water activities, I think one worthy contender is Swimming Stadium, which was the venue for 1952 Olympics swimming and diving contests and these days is open for the general public for a modest fee. And most (if not all) these places do have a sauna if you are looking for one. To continue the theme of Olympics, the Helsinki Olympic Stadium might interest you, the stadium tower offers nice views over the city and there is also a sports museum. And as you mention soccer, I think it is worth mentioning that July 11th to 16th there is the big youth football tournament Helsinki Cup. It might not be possible to join the teams participating in that competition for one day, but at least it would be possible watch the matches on various football fields around the city. Friday and Saturday will be the days for the finals, which are going to be played in Töölö near the Olympic Stadium. I guess the above is more than you can cram into a single day cruise visit, but I hope I gave some plausible alternatives to spend some time in Helsinki (and possibly neighbouring cities). And regarding snacks, I think simple and fairly healthy options would be picking up some fresh fruits and/or vegetables from a market vendor. July is the prime season for strawberries in Finland and peas (sold in pods) are a popular choice. And if you pick anything to eat from the Market Square, be aware the local gulls have became quite talented in stealing food.

When I last checked, Ireland was outside of Schengen area and Denmark part of it, thus there will be passport control when travelling between these two countries.