I have the same problem forgetting my bags! I've never bought one b/c I can't remember to use the one that dh bought. And b/c I can make them for less than the $1-2 that the store charges, with the stuff I have on hand.

What I do when I use sheets to make things that need to be sturdy is: 1) make sure they're not worn out to begin with. I use really thick sheets, high thread count, and 2) I double-layer them. Also, on most of the tote bags I've made, I make straps that go all the way under the bag, not ones that just attach to the top. This way they'll never rip off, and they'll help support the weight of the bag. But I don't use totes--I've just made them for fun--so I haven't actually used them. I've used ones like them before, though, and I think they're as sturdy as a tote bag could possibly be.

Also, someone was talking about the recycled materials movement. It's a HUGE trend right now to use recycled clothing and fabrics to make new things, lead by the girls' pillowcase dress item. Search it on sites like etsy and you'll be amazed at how many people are proudly advertising that their products have "back stories" or something like that. But it has to be in perfect condition. Which any fabric that I use to sell things is.