It depends on a few things:
1) How much money are you willing to spend per use and on equipment?
2) How often will you be wearing this costume?
3) What percentage of skin are you covering?
4) How much time do you usually have to prepare?
5) Do you have to drive somewhere painted up, or can you do it at your location?
6) How long do you expect to be this color?
7) What other difficulties will you experience with colors/brands?
I will try to answer each of these questions for each type of skin covering product. Additionally, if you have Photoshop, you can tidy up professional or even snapshots pretty easily. If you don't have Photoshop, please don't download it illegally, and don't ask me where you can do so - I will not help you do this.
Step 1: Tools and equipment
Suggested tools, at minimum:
Small baggie of wedges, 10 or so
Spirit gum remover
Black mascara and eye liner, neutral lip gloss
Black pencil and shadow
A set of around 15 brushes include a wide eyebrow brush, a kabuki brush, brow brush and wide and narrow flat brushes
Spare eye shadow applicators and lip brushes
Hair pins and ties
Cold cream and/or facial wipes
False lash sets
Spare bottle of contact solution and contacts case
Small tube of concealer
Small bowl with airtight lid, for mixing
Travel-size Q-tips case
White pencil and white shadow
If painting your feet, legs or other large portion of your body, put towels on the floor, toilet and sink. If your'e in a hotel, call for extra towels - the hotel staff like cleaning make up less than taking extra blue tinted towels from your room.
Something I cannot say enough is: do not buy cheapo make up when buying colors for costuming. Feel free to pick up cheapo stuff for color tests, but don't use only them. I try to buy makeup made in the US, and that is cruelty-free. Try to buy unscented makeup when possible. You won't use your shadow brushes as often as your regular makeup, so make sure you dispose of them once a year and replace with fresh ones, even if you haven't run out of a particular color. Your brushes can become bacteria nesting grounds, so treat them well and keep them clean between uses.