Doulas will find that some or all of these things useful to a laboring mom. The contents of your birth bags will, of course, vary. You'll stock your own birth bag with whatever is most useful to you in your circumstances. These supplies can be gained over a period of time, the only things you really need at a birth are your two hands and loving support, the tools just come in handy every now and then.
Most doulas use a large canvas bag or a small to medium suitcase on wheels.
There are times when only the Doula's presence is needed in the labor room, and she is not being asked to actually participate in any physical activities.