Honestly, I'm so used to grabbing a Burger King on the way to visiting in-laws (1.5 hour drive) and then timing our departure so we can be home for dinner, that it wouldn't enter my head that other people don't do that.
Because on the flipside, it's rude to turn up to someone's house if they haven't invited you for lunch/dinner, and expect them to feed you because your journey aligned with lunch/dinner.
That said, I personally would always make sure there's cake and biscuits for planned guests. But not because I think it's on me to prevent someone from starving if they're here between 2pm and 4pm. I'd do it because manners.
That's why I said the OP was unreasonable. I think it's unreasonable to expect your host to prevent you from 'starving', if you weren't invited for lunch or dinner. The title of the thread is 'AIBU to expect a snack when visiting someone's home for a few hours'. Yes, I do think it's unreasonable to expect anything.
I also think it's unreasonable not to ask for a bit of something, or go out to the car to get a snack, and not go for a meal afterwards just in case they happened to decide to go out to the same place. This whole thing is weird.
If I was the host, I'd have got a cake in.
If I was the guest, I wouldn't expect anything outside of mealtimes - I'd appreciate it, but not expect it, not go without lunch and be weird about dinner because I expected a snack. That IS very English of me, I think.