Hand it in to the local police station.
Throw it to the ground in disgust, at least somebody will be relieved of the burden of money.
Check the photo ID to see if it's somebody cute, then use the wallet to initiate conversation when you eventually find them. Score!
Seeing the wallet there saddens you, you grow emotional and feel it is your duty to return this wallet at all costs.
You return the wallet to them and give them some healthy advice about investment and banking.
You see the money and panic, what if it's a trap? The money could be fake, this could be a decoy. No, you can't take the chance. You leave the wallet there and hurry on.
"Has somebody lost a wallet full of money? Because I found the wallet!" You stuff the money into your pockets.
You feel enraged that somebody could be so careless and take the wallet for yourself to teach them a lesson.
You pick up the wallet and race around with determined strides and quickly find the victim, returning it to them.
Are you kidding me? You flip out on the guy throwing the plate of food into that schmoe's face. Storming out of the restaurant you yell behind you, "I'M NEVER EATING HERE AGAIN!"
You're too shy to say anything and afraid of upsetting the waiter, you finish your meal but leave no tips.
You feel sorry for them, they must have been having a hard day to have made such a mistake. You eat heartily and leave a tip to cheer them up.
You turn the food away, you'd rather not eat at all than spend another second of you life scarfing down second rate fodder.
You smile politely and request what you originally ordered again.
You do nothing, just smile and wave then pickpocket the goon when his back is turned.
You give him a waiting for dummies book, our labour force could do with some training and investment. You leave a tip hoping he uses it for good.
You check him/her out. If they appeal to you then you leave a tip with your number. If not then you request another plate of food and finish your meal.
You see no problem, what's the big deal? There's no need to make a fuss. You eat happily and leave a tip.