Such as an amnihook, internal lead, hmmm...what else do you pass around? Or don't you?
Curious as to what props you've found most helpful, too? Uterus, amniotic sac/placenta/cord, baby, pelvis, etc
I knew a CBE/doula who swiped things from the hospital when the chance arose, usually with a nurse's permission (amniohook, vacuum extractor, elastic bands used for monitors). You can get some disposable things from midwifesupplies.com. You can often fake it with some household item props. I've knitted a uterus and placenta and cord. Some kind of flexible pelvic model and baby to fit it is a must in my opinion, I remember first attending a class myself and the way it could bend to allow baby through really stuck with me. Otherwise, it all depends what your lesson/activity requires and what the goal is I suppose.
I "inherited" a lot of my gear from an educator who was retiring. I think she got most of her medical gear from hospitals (not sure if it was permission or not). I've also purchased a lot of teaching materials from Childbirth Graphics and my uterus & placenta I found on Etsy.
I agree with JamieCathryn that a pelvis + baby is probably the best thing to get first.