Okay here's my favorite super easy card "magic" trick. Works best prefaced by "I'm not very good at it but I hope it works"
You fan a deck and tell somebody to remember the card. Then ask them to put it back on top of the deck. Make sure to remember the card on top of the deck first. Then you give the cards a very shitty shuffle, but enough so they can see their card go into the middle of the deck. If you look really awkward and unskilled, this will work even better. The card they picked and the original top card should remain together.
You then just start flipping cards off the top of the deck, 1 by 1. at some point you will flip the card that was on top of the deck, meaning the card just before it is the card in question. Keep flipping a few cards. Then (make sure you look hesitant and unconfident), say "Okay if the next card I put on the table is your card, you down your drink. If it's not, I'll down my drink" If your performance has looked shitty enough so far, they will be sure to agree, since they already saw their card be flipped.
But instead of flipping the next card, you go through the pile, find their card, and put it back down on the table.
I've done this one before and it's always worked for me. The one difference I do is after they put the card on top of the deck I give them the deck and tell them they can cut it as many times as they'd like. By cutting the deck it's incredibly unlikely they'd separate their chosen card and the top card. Plus it makes them think they have more control over things
That's risky depending on how adamant they are about cutting. If they're cutting a random spot each time, at 10 cuts there's an ~18% chance they've split the two cards up. Your odds are 50/50 at 35 cuts.
Wow I love that you did the math! That's really surprising it gets to 50% relatively quickly how neat. I can definitely say no one ever cut more than 10 times when I tried it but I can certainly see that happening if someone wanted to have a laugh with it