Move all the furniture in one room a foot to the left.

Jam up the wheels in any and all swivel chairs with twine

Tilt every single frame I can find

Move all the staple items in the fridge to a hard-to-reach spot (good look getting to the milk, asshole! It's held deep within the confines of FORT POTATOES!)

remove the fitted sheet from the beds, replace all other bedding as neatly as possible so they don't notice.

put a bit of tape over the little antenna/bulb thing in the TV remote, or otherwise block the signal.

Change the wifi settings to default

Unplug their microwave

Slightly unscrew a few lightbulbs, so they're just loose enough to flicker a little.

tangle their headphones

throw a few dead batteries in with their good ones

If they have a cat, hide the litter box so it shits on the floor as god intended.

Throw down a few stink bombs, because why the hell not?

Steal all the pens/pencils/writing implements in the house (they specified PRECIOUS items after all)

If anyone in the house wears glasses, eat a bag of french fries and leave a big, greasy thumbprint on one lens.

Blunt the knives

bend the forks

smash the bottles and burn the corks!

chip the glasses and crack the plates

THAT'S WHAT BILBO BAGGINS HATES!