From Brotato Wiki
Item
Item is an in-game item that can be bought from Shop or can be found in a Crate. Most Items increase the Stats of the player while some of them provide unique effects.
Dynamite increases the % Damage of weapons with the explosive tag, and the damage of all explosions. This also increases the "non explosion" part of the weapons, such as the projectiles of Shredder or the damage of a Plank melee attack.
% Damage and % explosive damage stacks stacks additively. So if you have a Dynamite and +30% damage, your explosive weapons will deal +45% damage in total.