I'm a level 5 Druid and my group consists of me, the DM and a level 5 fighter. I am unsure of what feats my companion should have. I'm having it fill in the role of a scout. It knows common, and its skills are acrobatics, intimidate, sneak, and survival. It has 4 tricks: attack, defend, guard, and track. It has 3 feat slots, what feats should I fill them with?
Feat Support For This Is Really Poor
Like, really really poor. 'Scout' is not a terribly supported archetype, and Pathfinder does very little to help it. You could technically do Skill Focus (Stealth), I suppose, but that only really helps so much. I'd spend the feat slots on combat feats to help it when it's fighting alongside the Fighter.
But the item support is pretty great!
Masterwork tools are pretty cheap – talk to your DM about masterwork tools in the form of armor modifications to boost its Stealth. You might wanna shuffle the skills around to include Perception if it's scouting, and then you can tag a masterwork item for that as well, boosting the two key skills. Got extra money? Buy up some armor enhancements to make it stealthier, or a wisdom-boosting headband to make it more perceptive (and able to track better, if you keep Survival as a skill). If your companion's intelligence is three or higher then it can use items with a mental or command-word activation (since it speaks Common) so look into those to see if any can help you out – something like Wings of Flying could greatly help!
Do remember that non-humanoids pay special costs for armor – see the tables in the equipment section of your core book. Or here.