If you have tattoos that are either always visible or easily visible if you wear loose clothing, you may want to consider keeping a coverup kit at the ready. No doubt you take pride in your tattoos and don't want to be around people who actively dislike them. However, chances are that you'll eventually end up in a situation or two where you need to be sure the tattoos are not visible no matter how much you like them. Sometimes, a little coverup makeup is all you need, such as for tiny tattoos. But if you have larger tattoos, especially ones that are in areas where clothing can regularly hit the tattoo, you need a larger temporary tattoo cover up kit.
One of the biggest reasons to keep a full coverup kit is if you travel internationally. Many countries don't view tattoos in the same way the United States does, and sometimes the reasons are highly specific. Japan is a good example; tattoos were originally worn only by the Yakuza, or the Japanese equivalent of the mafia. Even though modern attitudes, especially among subcultures, have relaxed a little bit -- and most people in the country are aware that tourists may be sporting ink -- you will still find adverse attitudes and be banned from certain places like many public baths.
If you know you're going to be walking into a situation where your tattoos will be less than welcome, then you can put the coverup kit on in the morning and wear it throughout the day. Look for kits that have a skin-like layer that you place on top of the tattoo; while you'll still need some coverup makeup to make the layer's edges blend with your own skin, this will be a lot easier than adding lots and lots of coverup makeup all over a large tattoo.
Companies are becoming more open to having employees with ink that isn't blatantly gruesome or offensive, and sometimes showing your tattoo in a job interview is a good way of telling whether you'd want to work with the company (if your interviewer recoils, maybe you want to look elsewhere, right?). However, for most interviews, it's better to play it conservatively first. If you're not sure of how the company functions, covering up the tattoos is best. You never know; you might walk in and find the receptionist inked up. But until you get a better sense of what the company wants, play it safe.
Granted, if you're not interested in acting, this won't apply to you. But if you've been thinking of getting involved with community theater or going back to school for a drama degree, start learning how to cover up the tattoos now. While drama schools and theater troupes are full of people who like tattoos, the characters you play are not always going to have them. It will save you a lot of time when getting into costume if you can apply a large skin patch to cover up most of the tattoos quickly.
You've got a number of different choices for coverup kits; talk to friends who have tattoos as well as tattoo parlors to get suggestions for ones you should try. Give the kits a test run to ensure the results are satisfying.