Finding cash on the street

I'm on holiday. It is now the morning of day 3 or day 5 if you count the first weekend as part of my holiday. Yesterday we visited the big town near us and spent a lot of money. The 1st item on our shopping list was a new bed for my son. The bed he's got now was a godsend, it was given to us by friends but is one of those with a ladder and a desk. Making the bed takes a real effort because there is one corner that is really difficult to get to, against the wall with not much ceiling clearance. The 2nd item was a replacement fridge. Our current fridge was inherited when we moved into this house in 2011. Although it still works, there is a problem with the thermostat. We've had to cycle blue plastic picnic chiller box  blocks between the freezer section and the fridge for over a year now. The glass shelves have pools of water we have to wipe because of the thin layer of ice melting on the surface of the blocks. We have to regularly throw food away that hasn't lasted in the fridge. Milk goes off quickly. The trouble with a fridge replacement for us was that the choice was limited to one make and model. It has to fit into a cupboard that's integrated with the rest of the kitchen. So we had to spend a lot of money. I think it will be worth it though. It has the highest energy efficiency rating and it is a frost free model, so we won't ever need to defrost it. It was a lot of money though, however, we need a fridge that works and we have the money because we didn't book a summer holiday this year. A fridge is more vital than a holiday.
Anyway, now I'm on to the main subject of this post, what would you do if you found some money on the street? My wife and I went to the big town in the morning but had to go back in the afternoon with some measurements of the doors of the cupboard the fridge lives in. On our first visit we parked easily, another car was just leaving as we arrived and I could drive into the space. It was in the cheaper parking zone. Now, on our second visit I could not find a space in the cheaper zone, so I carried on round to the higher rate zone and parked close to one of the parking meters. We were exchanging some DVDs and videogames as well, so the shorter distance to the shopping centre actually was a good thing. As I walked to the parking meter I spotted a folded 20 pound note on the floor. The area near the meter had only 2 or 3 cars nearby and they looked like they were there some time. Without any idea of whose money it was and no way to find out, my wife and I decided to pick it up and keep it. I think our behaviour was dictated by the ridiculously slim chances of finding the person who lost it and also the value being small enough to be welcome but nowhere near life changing. If we'd found a whole wad of cash I'm not sure what we'd have done. I think I would have felt the need to take it to the shopping centre information desk. Maybe they could make an announcement but how would they know that the person making a claim for it was the rightful owner? How would the police know, if we took it there? Apparently, if you find cash on the street and hand it in to the police, you have 6 weeks before you can claim it as finders keepers.