Mabel got out her felt board to play with. She decided to wear the felt board, noticing that it tied shut with attached strings and deciding that her always-compliant Grandpa could make himself useful by tying those strings behind her back. Then Mabel manipulated the elastic band (which also holds the felt board shut) until she had created a sort of harness anchored behind her neck and securing the corners of the felt board garment.
Still wearing the felt board, she then dug out several inflatable toys that had been tucked away uninflated toward the bottom of a new storage bin.
In the final picture Mabel is suddenly inspired to hand over the deflated monkey to her Grandpa and urge him to blow it up.
In the end, he blew up all the inflatable toys.