Not so much the important stuff. Ever since Kiddo was young, we taught him that things like keys and our phones/wallets were absolutely off limits. But he had a couple secret stashes of 'ick' under his bed. ("Ick" is a concoction of water, soap, toothpaste and chalk or whatever other disgustingness...) For some reason, he liked making these 'potions', and then we had to talk about what would have happened if they had tipped over and spilt. We discovered the 'ick' after likely a couple of weeks. Reeked. Pure grossness.
Oh, and he and his friend were sneaking bits off the gingerbread house a couple years ago... decided to eat the candy bits in the bed and under the bed... that was a total PITA... stripped the sheets, had to vacuum under his bed (which is a futon, so the whole heavy thing had to be moved)... Yes, under the bed certainly has some sort of attraction for mischief!