I once found a lost cellphone, and after its owner called it, we arranged to meet and I returned the phone. The owner's reaction was very similar to what you describe. I refused any reward - it seems natural to me to just return it - but later that night (it was a Friday night and I was out for drinks with friends), we bumped into him in a winery, and he ended up buying me and my friends a huge jug of very good wine, out of gratitude. :)