A standard 16.9 fluid ounce bottle of water weighs 17.6 ounces, which is equal to 500 grams. You might also find some cans in your cupboard this size.
Another option is to use coins. A US nickel weighs exactly 5 grams, so 100 nickels weighs exactly 500 grams.
Pennies weigh half as much, 2.5 grams each, so use 200 to measure 500 grams.
500 grams is .5 kilograms. In the video below you can see what burning 500 grams of thermite looks like.