I'm a hand piecer and almost NEVER leave the house without a block or two somewhere on my person to put together.
I love to do samplers, so when I am making one I put all of my pieces for each block in a seperate zip lock bag along with any piecing directions. If you're doing a design that all the blocks are the same it's not quite so bulky.
I have a small box that holds my small "snipping" scissors, I pre-thread 2 packages of my favorite piecing needles onto a spool of thread and that way don't have to try to thread needles "on the go". I have a little packet that holds just a few pins.. usually don't need more than 4 to piece blocks. You might want to add a seam ripper, but usually they are not necessary for hand pieced blocks, and I just add one of those huge yellow ball headed pins to pick out stitches that have gone astray. and all of this will fit in a nice zip lock bag, and the bag protects everything also. have a super time and happy stitching.