Build a 24hour clock with a seven segment display. That will keep you busy for a couple of hours.
An order-sensitive combination lock with consequences (lava released via piston from above where you press the button, maybe?)I enjoy seeing consequences for when people try to brute force through redstone obstacles, like what you did with the minecart that sends you to your death if you throw a cart on. That was good stuff!P.S. Are there any more room on your server? Would love to build some cool things with you.
An game of tic-tact-toe(AI enabled). might keep you busy for days together