Giving red envelopes filled with coins is a custom at Chinese New Year (which starts January 26), designed to bring good fortune to the recipients. Here's how to share the luck with dinner guests.
1. Rubber-stamp a red envelope with a New Year's greeting -- in any language -- using a gold-ink pad.
2. Fill it with change, and then lay it on a folded napkin wrapped with a band of patterned paper.
3. Tie in back with gold cord.

If you don't live near a Chinatown like I do, you'll find that Hallmark stores carry a small assortment of Chinese New Year cards and red envelopes!
Where do I find traditonal red envelopes?
Another greeting besides Gung Hei Faat Choi is Sun Taai Gin Hong....meaning have good health.
I am so glad you mentioned the amount not having a 4 in it! I have a Chinese exchange student this year and if I had not learned the traditions beforehand I would have no clue. I think before we decide to participate in another persons traditions we should know everything about the tradition we can! We would not want to offend anyone.
I am Chinese. The adults give mostly to children. Yes, the amount is very important. It is also customary to have an orange or tangerine for each guest in even numbers.
Cantonese only have married people giving the unmarried money envelopes. Married get no envelopes. Only household helpers or delivery men, etc.
If you are giving the red envelope to someone who is Chinese, be aware that the amount is significant. It must be an even number, not odd, and cannot be 4 as $4 since that represents death and is given at funerals. This is a great idea, though.
Step1Say in Chinese (Cantonese): Sun nien fai lok (meaning, "Happy new year"). Also, say: Gung hay fat choy, which means "May you become prosperous.")
Step2Say in Chinese (Mandarin): Xin nian yu kuai.
Hi PhotoGal, in Mandarin Chinese it is: "Gong-chi fa-Chai." :)
We go to a Chinese restaurant quite often, maybe I'll make a couple of these and give the waitress her tips in them. Wish I knew how to say Happy New Year in Chinese. If that is what it says on the photo above, it's too small to read.