As a Canadian who spends a lot of time at cons in the US, I always aim for one fun item like popcorn (or a local treat), and water for the duration of stay. If there's a mini fridge in the hotel rooms, then things get fancy with the convenient store goods like salads.
I try to pack snacks in luggage to keep costs down now -a fave nut mix, granola bars, beef jerky, things like that. Some friends and I have gotten good at doing one main meal a day at conventions and the rest of the time it's truly just snacks.
Protein bars are good for small travel items you can toss in a day bag while out and about in costume too.
(Those US space brownies are good, btw...)
One tip that's saved a lot of people - keep electrolyte packets on you. Or plain old Gatorade/water.
Gum, mints, or candies are also good to have something to chew on when stuck in elevator-con, or stairwell-con. (This has happened to me so many times at DragonCon over the years, lol) Seriously, I always have something on me because you never know when or where you'll end up in a traffic jam of people, especially during summer months.