I can't remember Boston prices, but at KC at U.S. Nats a few weeks ago, a hot dog (which was kind of a specialty hot dog topped with cheese and bar-b-q) was $9.50. Think a regular hot dog was $7.50 USD. Not a coffee drinker, but pretty sure bottles of Pepsi and water were $5. My friend bought popcorn, and I think it was $7 (it was a BIG container). I'm just glad they take credit cards at Hartwall which will hopefully make my life easier and I won't run out of Euros and have to change more money.
In your place I would find out which are the exact credit cards they accept there, sometimes even American Express card is an unfortunate exception... And whether the credit cards apply to fast food, etc.?
http://hartwallarena.fi/en/visitors/food-drink/fast-food

Yes, please, warmer next week 

}}, and other fun stuff too. The trick is to not get too hung up on looking at devices and end up missing the live action.