Not for travel, but to keep qult blocks in before I sew them all together a quilt top, I use a set of stacking 12" square plastic boxes made for storing Christmas ornaments, that I got at a garage sale for $1
Each box is about 5" tall, and is the lid for the one underneath. The stack of 4 boxes has a lid with a handle in the top box.
I put the blocks in one, and pieces for the other blocks in process in the one under it, so I can keep 2 projects all contained.
Those 2 gallon ziplock Freezer bags work pretty well also.