From the US, I'm afraid hotdogs or lawyers don't store well in backpacks
Wine is a big fad there... wine from oregon or some unusual place in the US might be a hit (e.g. Texas wine) ... but then you're probably not 21+.... (also not sure what you can actually import so check customs rules)
The chocolate idea isn't bad as there are some excellent "micro-brew" chocolatemakers in America.
The more you find out about your host family the better, but you might look for something that your home town or region is known for ...
that would be an icebreaking measure as they will be curious about your home area. Obviously you'll have to decide how much to spend, but something that implies thoughtfulness and uniqueness rather than a "gift card"
is the direction you want to go here...
The more I think about it, the harder it gets.... mostly food items come to mind and they're either hard to transport or possibly against the rules. Here in Oregon, we have a store called "Made in Oregon" that sells locally made items, perfect for such a situation. Your state may have something like that.