You can try this, I haven't tested it, but it's a start.
random_items = {
{5,2112,1}, -- 0.5% to get teddy bear
{20,6512,1}, -- 2% to get santa doll
{40,2114,1}, -- 4% to get piggy bank
{80,2111,5}, -- 8% to get 5 snowballs
{80,2688,8}, -- 8% to get 8 candy canes
{80,2110,1}, -- 8% to get doll...