French fries is the standard German pool food. Like, nowhere else do you see stands selling nothing but fries (with ketchup and/or mayo, of course). And they just don't taste as good anywhere else, I guess it's the chlorine in the air making the salt taste extra special without actually tasting more salty.
I'm Dutch and I have similar memories. Fries, crisps, and/or ice cream used to be a quintessential part of the pool visit. Kinda makes me nostalgic thinking about it. After all that moving around the fries were an even better treat.