"Carry at least your lip color," Alex says, "as that's what'll wear out the fastest and need to be touched up the most." If you use good quality face and eye primers, everything else should stay in place.
Alex also advises keeping some oil blotting sheets on hand. "If you don't want to keep piling on powder throughout the day, make sure you also have some oil-absorbing sheets so you’re not just adding on more and more makeup. You can switch on and off — an application of powder, then the oil-absorbing sheets, and so on."
Q-tips are another great item to carry around with you. Makeup can collect in the inner corners of your eyes, and you can use the q-tips to clean them out.