For my Superhero-themed June sensory bin I got Goo Jit Zu Marvel Minis and put them in Orbeez (I had some individual packs that I combined, but I’ll use the big seed pack for the future). Kids love these Orbeez! I only get them once a year (because they bounce EVERYWHERE and crush into mush) and I try to time them to a hot month since they’re super cool (in temperature, not the Fonzie kind).