From Brotato Wiki
When an enemy is killed with critical hit, for each Hunting Trophy the character has, the game rolls a 33% chance to give 1 materials (Just money, no XP, so lets call it gold). If there are 2 hunting trophies, it rolls twice. If there are 3, it rolls the 33% chance 3 times.
For each succeaful roll, you are given 1 gold. If there are 2 Hunting trophies, it can give 2 gold with 1/9 chance, it can give 1 gold with 4/9 chance, and not give any with 4/9 chance.
If there are 3, it could give 0 to 3 gold depending on chances.
The result is that the average amount of gold earned is doubled if you have two, trippled if you have three.