When designing games it makes sense to have some physical objects to make the virtual world a bit more easy to visualize. This is the things i collect to help me imagene a world inside the computer.
Dice
Four sets of transparent dice with D4, D6, D8, D10, D12 and D20. Then get all the fun ones you stumble on.
Blank Cards
Paint or write anything on them and then use them to play with.
Card game sleeve
Use to protect cards.
Playing cards
Standard set of playing cards. So you can play solitaire when you are thinking about the game design.
Poker Chips
If you get bored in design meetings you can always play about cash.
Stands
Used to put cards in so the can stand up. Paint a monster on a card and put in these and you can have a cheap troops to move around.
Sand timers
Timers with sand.
Tokens
Use to represent something in the game. As many forms and colors and number of them as possible.
Counters
Used to represent numbers. Like number of hitpoints or lifes left.
Money
Play money.