*insert perverted joke here* xD
On the serious note: Give them the gift of KINDNESS! =D Making someone do a little more good is the best gift you can give.
You could fill each one with two papers which contain commands on them and one paper with the name of the person that has to do it.
Make the commands simple acts of kindness and give bottles to everyone. There is no time limit. The only person who has to know what you have to do is the one who got your bottle. It is not about bragging to everyone what you did, but doing something good just because it is.
DISTRIBUTE THESE INSTRUCTIONS TO EVERYONE ALONG WITH THE RANDOM BOTTLES THEY HAPPEN TO TAKE.
STEP 1: Take the command out of the bottle, read it and write your name bellow it.
STEP 2: Give the first/command paper to the person whose name is one the second sheet of paper. Keep the bottle and the paper with their name.
STEP 3: Do the command you got.
STEP 4: Write what happened on the back of your command and put it in the empty bottle you got. You can even put a picture or some "souvenir" that relates to the event. If you were rewarded share the reward, whether it's sentimental or material reward.
STEP 5: Give that bottle to the person whose signature was bellow the command. That bottle will be your thanks to them. It is them who enabled me to give you this kindness.
Don't overdo it. Ask things like: feed a stray dog, make a meal for the homeless person, visit someone who is alone, make someone laugh, smile, aid someone, teach someone etc.
Also make sure you participate. =)
WARNING:Make sure that your personal knowledge of some people doesn't effect your commands in a negative way. Meaning making them do something they feel too uncomfortable doing, or if the receiver of the deed feel uncomfortable. If you choose this it is at your own risk. ^^
PS. You can just use my text, I won't mind.