Why use paper bags as pattern paper?
A. It's sustainable re-use.
B. It's cheaper than pattern paper and much sturdier.
C. It's really convenient.
D. My inspiration can't wait for me to drive to the store to get patterning paper.
E. All of the above.

All of these answers are good. I personally like "E".

I've been using paper bags as pattern paper for years. Sometimes that's because they're around and no one has time to run out for a roll of paper. (Deadlines on TV shoots and rock star samples can get pretty hairy.) The tissue paper used for commercial patterns is flimsy and awful and gridded pattern paper isn't much stronger. And who wants to pay for it? Rosin paper rolls from the hardware store are great if you're making very wide patterns for things like Renaissance skirts and inflatable wading pool belts. Sometimes I need that extra width. But for most plain old clothing patterns, grocery bags rock.

I'm fond of Trader Joe's paper bags for hat, shirt and accessory patterns. The bags are sturdy and already made of recycled materials. Whole Foods bags are thinner and taller, so they're pretty good for pant and skirt patterns. Other chain grocery store bags seem to be both short and thin, but they'll do in a pinch. Any paper bag will do! If you don't have enough room on one bag, Scotch or masking tape is your friend. Make it a Franken-pattern by taping the flattened bags together. Just remember: tape does not take well to a lot of heat. Both clear plastic tapes and masking tape can melt and sticks to the iron. Iron out your paper bags before taping them.

Regular re-users, please stop here. You already know how to cleanly tear apart a paper bag. For everyone else, here's the step by step process in pictures.
Next time we'll make a pattern from a partially dissected top.