For those projects that go with us, we often have tons of tote bags. The problem I am having these days with "projects to go" that go into tote bags is that everything else goes into that bag, too. An extra skein of yarn or two, just in case I finish this project and need to start another right away. A complete set of crochet hooks, just in case. Several needles. A few patterns. Most of you know the drill.
I have had to downsize recently. I've found that those little zippered cosmetic bag sets work wonderfully well. The ones I am using are never more than a foot long and six inches high, plus about two or three inches wide. Frequently, they are sold in sets of three, sometimes nested. They have room for a full skein of yarn plus the project. They also have room for a mini-zippered bag to put inside the main bag.
I have seen a lot of these at most of the dollar-type stores. I really love these for projects on the go. There are great benefits to these bags.
I am limited to one project-to-go at a time.
The bag stays lightweight.
I am forced to finish that project before adding another one (the best benefit of all!)