Cafepress is an online enterprise where you put your designs in a media bin and then select what products you want them printed on. It's like zazzle.com.
You make a storefront and then people order the stuff. Cafepress tells you what the item costs, and you decide what your markup will be and then they pay you the commission. They take care of the printing and shipping and stuff. It's all very hands off.
The nice thing is it's better for short-run things than going to an actual print shop. If you are having an event and want to make shirts or stickers or water bottles, just put up the art and give people the link to your store and they can order what they want--no up-front costs to you.
My brother-in-law did something goofy last year and I put a funny graphic of it in an email to my family. My sister commented that it would make a great T-shirt. I threw it up on CafePress and they ordered shirts for the whole family.
The strange thing, is that Cafepress is now selling these things that were only available on their website on ebay and Amazon now.
Whenever there is some interesting or funny news event, I always go to cafepress and do a search. There are usually some funny shirt ideas that people put up.