Maybelline Lash Stylist is also my pick! I did many experiments with other mascaras, but their v-comb gives perfect results (no clumping!) and adds just the right amount of length.
Other essentials would be:
Concealer - for those problem areas
Blush - for a fresh summer look (I also use it as eyeshadow!)
A quick swipe of mascara and some lip gloss, and you're ready to go!
As for tools, you don't need more than a big fluffy brush for the blush, and tweezers to keep your brows in shape.
Those are my essential items in summer. Once you are comfortable with that, it's easy to add to the list with foundations and eye shadow colours, different eye liners and a variety of other goodies to experiment with :)