slight enough to make toilet tissue seem substantial.
And, nearly everything here is slight enough to make toilet tissue seem substantial.
Items like sink water filters, toilet deodorizer, RV/marine toilet tissue and holding tank cleaner go on sale at camping supply retailers and mass merchandise stores from time to time.
As a rule, if a toy can fit through the center of a toilet tissue tube, it is too small.
If you end up with lots of jars of different things, you can bundle all of these together in a box or basket (or even stand up toilet-tissue rolls in the box and use them as dividers-decorated, of course).