Slice of Cake
Usable when placed 'Stuff your face. Stuff someone else's face. Whatever.'
50a buff you carry as furniture
This is not something you eat. You put it down, activate it, pick it back up, and walk away with the buff still running. It never gets consumed and there is no cooldown, so once you own one you have a permanent movement and mining boost available whenever you can spare two seconds to place a block.
put it in the mine
Digging is the obvious use, since the movement and mining bonuses both feed the same activity. Set it at the top of your shaft or in a niche in whatever tunnel you are working and top up whenever you pass it. On a server anyone can use the same slice, so one sitting in the base covers the whole team.
getting one is the annoying part
The Party Girl only hands it over during a party the game throws on its own, and only to whoever reaches her first. Setting off a party yourself with a party center does not count, which catches a lot of people out. If you play with others, settle who is taking it before somebody sprints across the map, because the rest of you are waiting for the next random one.