I haven’t made a knitting gadget post in a long time. Here’s a frugal crafting tip, echoing something I posted in 2004.
Save those little, rectangular plastic clips that seal up bags of commercial bread, pizza dough, bulk food purchases, and other groceries. They are very handy for knitting and crochet. Here are some uses.
Stitch markers. Very obvious. All of the standard and exotic stitch marker tricks can be done with these, marking repeats, separating design panels, using them to delineate a group of stitches that will be added or decreased away, using them as an in line abacus to keep track of row or pattern repeat counts.
Progress tags. Like fancier plastic clip style closeable markers, tags can be fastened onto in-progress knitting to mark spots of interest, like centers of pieces to be matched together later while seaming. Because tags are larger than commercial clips, and disposable (in my house, a renewing resource like wire hangers), they can be written on with a Sharpie marker, for one-use notation.
Seam basters. Use the jaws of the tags to hold pieces together when seaming instead of pins.
And here you see another use: pick-up tracking. I have a lot of stitches to pick up along the edges of my current project’s center entrelac panel. The desired number works out to ten stitches per edge triangle. It’s very easy to lose track, an annoying to constantly repeat the count. But if I clip a tag onto the needle, pick up ten stitches after the tag, then I clip it and repeat, the process is relatively painless.
String-Or-Nothing 
Do you use them as is, or do you file the sharp edges/points before use? I’ve feared they’d snag stitches when the project is tossed into its bag for transport.
I use them as-is. That being said, I tend to use them on larger garments, not on fragile lace. Most sweaters, pullovers, cardigans I do tend to be sport weight yarn or heavier – snagging has not been a problem.
On a similar thread, this reminds me that I recently came up with using string tags (such as http://www.walmart.com/ip/Avery-White-Large-String-Tags-100ct/17163665) for labeling the yarn in my stash. This can be helpful when ball bands have fallen among the dust bunnies under the sofa, but it has other purposes too. You can write down things like where/when you bought it, etc. — while you still remember. When I get out my scale and calculator to estimate how much yarn is left in a given ball, I write that info on the tag in pencil (for easy updating after I use some of it). Avery makes string tags you can put through a printer, which might be handy for spinners and dyers.