So, this is my shot at a SAHM-ish toddler activity.
I have a collection of clear plastic containers-- water bottles, juice bottles, snack containers. I filled them up with various things-- some noisy, some pretty. E has glittery water, water with beads, bottles with just beads and with bells, ribbons, sequins... you name it. They're dirt cheap and disposable when he bangs up the bottle/container too much. And, the possibilities are endless-- every time I take a trip down the craft aisle I get more ideas.
For added safety, I'd suggest putting a little adhesive around the cap once the bottle is ready. You don't want your little ones getting those caps off and eating whatever treasures you've put on the inside.