As far as H.O.P. (Hands Off Parenting) goes, the ice cube treasure hunt was by far the most successful activity we have ever done. It also was the easiest set up and clean-up. Note, that this does need to be prepared at least 24 hours in advanced.
(I may have given Mila a chocolate cake pop)
Plastic tub (purchased ours at the dollar store)
Small plastic toys or household items
Hammers (toy hammer or light weight household hammer)
Some ideas for the treasures: LEGO blocks, play food, action toys, kitchen utensils, straws, barbie accessories, dice, pom poms
Place items in the bin and fill with water about 2″ from top. Seal with the lid and place in the freezer. We froze ours overnight and it was ready to go in the early afternoon.
The block slid right out of the plastic bin. Then I equipped the girls with hammers. The wood hammers seemed to fray from the water so I may pick up some small metal light weight hammers because we definitely will be doing this again.
They spent 45 minutes hammering at the block while I took work calls and designed a gym while sitting outside overseeing them play. They literally got excited every time a new item was pulled out.