Knitette

I use those thin colour coded chopping boards - red for meat, green for vegetables etc. They're usually sold in packs of five in the catering section. Easy to cut and inexpensive too.

GrannieAnnie

I use a heavy iron on craft backing. I do 3 or so layers, cut just inside the seam line.

pspeebles

I usually go to WalMart and look in their kitchen utensils area for the pack, of 6 I think it is, plastic colored cutting boards.
Those are easily cut with utility scissors, and with corners rounded seem to be perfect stiffening material for tote bags, purses, and clutches. While leaving the purse (or item) totally washable although I hang to dry for fear the dryer will melt the cutting board.
The needlepoint net idea is really good but hang dry is what I would do if I use that as well.
There are also programs to create fabric labels for homemade sewn items that are washable too.
I even found a company that makes them for you and it isn't costing a arm and leg either. I love this because I make items for my grandbabies and can put who it is from as well as washing instructions.
A friend of mine actually uses her embroidery/sewing combo machine to make her labels and then sews them right into the item. She picks up white pillow cases from thrift stores, goodwill stores, garage sales etc and has a cardboard rectangle that she uses to cut the "label" out (from the pillow case material ) with so that it is large enough to hem, embroider, and read!

Bobbielinks

This is what I have done.