Some tips for people thinking about hauling groceries home:
1. I like paper since the bags stand up nice and straight
2. If you get plastic, then knot the bags at the top so things don't fall out
3. Make sure you balance your bike left and right, front and back
4. If you have a spare jacket or a sweater with you, put it under the eggs and beer
5. When you go through the check-out lane, group all the cans, all the jars, and all the breakables.
6. Ideally, each paper bag will have some weighty cans or jars in the bottom and some lighter/breakable things in the top.

If any one else has some tips, put them here.