I just made some and filled them with Steel wool it is supposed to keep your needles and pins sharp

what health consequences for the crushed walnut shells

I used crushed walnut shells in one i made and it seemed to corrode the ends of the pens, they are quite dull. I won't use them again! I was really disappointed.

I was about to suggest steel wool too!

I think issues with walnut shells would be the dulling possibility as well as how many people are allergic to nuts now-a-days.

Walnut litter.

It gives it weight and keeps the pins sharp.
http://kaytee.com/products/walnut-litter.php

I also like wool or a combo wool and walnut litter.

Wool if it is natural and has any lanolin on it will keep them sliding.

The opposite it keeps them sharp.

Other alternative options would be sand or saw dust but you really need to be sure the fabric has a tight weave. I have pin cushions made with both of those too. I would be concerned from what wood the saw dust is as many wood products have chemicals in them.

Wondering what fabric to use for sand?

I'm not thinking for pin cushions ... rather for a small sandbag to weight down a goose neck lamp, so it does not tip when extended where I want it.

Have the sand ready ... and would like to keep to all fabric instead of a plastic bag, as eventually it will get holes and I'll have a sandpile! :D

For sand I would suggest good quality cotton canvas. It works for sand bags.

A lot of people on the board that make pin cushions for exchanges don't use them as a pin cushion, rather a collectors item. for those I stuff with poly fil. it gives the pin cushion a nice look. But then again, most are used as eye candy. I put my pins in a box, all my cushions are for the shelf only.

see what the recipient is using it as.