Kitchen skills give two types of boosts: "Food" skills, and Felyne skills. The food skills give health (based on the combined stars, up to 50 max), stamina (50 max as well, based on Freshness), and one other skill (Attack, Defense, Resistance, Tipsy, etc.)
These Food skills will always stack. Without the Felyne Foodie skill, you will also lose them upon death.
The tricky ones are the Felyne Skills. Some are unique, in that they provide a skill that can't be gotten any other way, such as Explorer, or Carver. These don't stack, because there's nothing to stack with. Others are binary buffs, in that they either work or don't, such as Heat Res (Armor Skill), and Firewalker. Both allow you to walk on lava edges with no damage. Getting both does nothing, because there's nothing to improve.
For the rest, they will stack, up to the limits of whatever is being increased; both Gathering and Felyne Gathering up the chances of hitting maximum node gathers, but they can't do anything beyond that. Same with Speed Sharpening and Polisher; one swipe is the minimum, so Polisher adds nothing.
Those that add to numerical values will be tested as I can, but current observations show that as long as the internal limit isn't hit, they do stack. As to what those maximum values are, that differs depending on the skill. There has to be a non-0% chance of things happening (such as Whim and Woodsman combining), or gathering would be trivial, as nothing would break, and you'd never need to replenish your pickaxes or bug nets.
I have tested these, and will add as I test more:
- Firestarter, Waterbearer, and the other elemental skills DO stack.
- Specialist does stack with Status Attack.
Tools don't have a set number of uses, but instead has a chance to break every time you use it. The higher tier tools just have a lower chance of breaking, which normally results in them lasting longer. You can decrease the likelihood of bug nets and pick axes breaking with the Whim armor skill, and the Felyne Woodsman kitchen skill.
There are three tiers for bug nets and pick axes. In order from lowest to highest they are: Old Bug Net, Bug Net, Mega Bug Net, and Old Pick Axe, Iron Pick Axe, and Mega Pick Axe.
Best Answer
The Expert skill (from armour) stacks with the natural affinity percentage on weapons. For instance, I've used the Arko Nulo bow (5% affinity) with Diablos armour (Expert +1) which gives me an overall affinity of 15% on my status screen.