The thing Rock Paper Scissors does that most games can't is function without anything. No board, no cards, no dice, no phone. Two hands and thirty seconds. The games that come closest to matching this are the ones that share the hand-based, no-equipment structure — and a few that add minimal props to create stakes or variation.
Thumb wrestling is the most direct physical equivalent. You lock hands, thumbs up, and try to pin your opponent's thumb for three seconds. Unlike RPS, it involves sustained physical contact and favors larger hands slightly, but the entry cost is the same: zero. It works anywhere RPS works and adds a physical engagement that pure gesture games lack.
The addition and multiplication games are RPS's math-drill cousins. Both players show a number from zero to ten with their fingers, and the goal is to shout the sum or product before the other person. This is genuinely educational, works well with children learning arithmetic, and has the same instantaneous start property as RPS. The math game also scales: you can increase the number range or shift from addition to multiplication as skill develops.
Finger spelling is more cooperative than competitive. One player draws a letter on the other's palm with eyes closed, and the receiver guesses what was drawn. It works for single letters or short words. The game builds tactile awareness and works in settings where loud play is inappropriate — classrooms, quiet waiting rooms, situations where two people need something to do with their hands but can't make noise.
The hand slap game — one player's palms up, the other's hovering palms-down above them, the bottom player trying to slap before the top player pulls away — is almost purely reflexive. There's minimal strategy, though experienced players develop a read on their partner's hesitation patterns. It's extremely fast, causes occasional mild stinging, and is very funny in short bursts.
Ninja works with four or more players standing in a circle. Players take turns making one ninja-style movement to try to slap a neighbor's hand. Once a hand is eliminated, the game contracts. It's chaotic at large group sizes and worth playing once with the right crowd.
None of these replace Rock Paper Scissors. They're for the situation where you've been in the same waiting room for two hours and need something different.