DH and I are feeding our neighbours' cat while they're away on holiday. We've been neighbours for over a decade and while we don't live eachother's pockets, we have DC the same age and I'd class them as friends. I wash up the cat bowls in between feeds and noticed that they were nearly out of washing up liquid, so picked up a new bottle while we were at the supermarket. DH is squirming with embarrassment and trying to convince me it's a weird thing to do. I think it's completely normal and just a nice thing to do.
YABU - your neighbours will think you're weird.
YANBU - it's fine.