I'm not a Project 10 Pan expert by any means, having only finished 2 measily products in the past one and a half months, but I have discovered a few loopholes in the system while continuing on my treacherous, makeup-purchase-free journey.
Keep in mind, though, that my personal P10P goal was to specifically use up 10 makeup and/or nail polishes (although I'm not really anticipating using up any nail polishes) and not buy any more of those products until then. Someone who is attempting a classic P10P may not find nearly as many loopholes as I have...which is probably a good thing ;)
Perfume:: Clearly fair-game since it's neither makeup nor nail polish, I indulged myself in a quick pick-me-up with a rollerball of Stella by Stella McCartney EDP. I'll still give myself a pat on the back, though, for resisting and not shelling out too much money while on P10P and getting the full-size bottle.
Skincare:: I asked on Twitter whether people considered Origins VitaZing a makeup or skincare product and got several extremely iffy replies. Then, when I went to take a look in-store, I noticed that it's clearly marketed as a moisturizer, therefore being fair-game, and therefore finding it's way into my shopping bag.
Freebies/Samples:: I actually picked up all of my foundation samples prior to starting P10P, but I think that samples and little freebies (like Sephora 100-point perks) are a good way to curb your new makeup cravings. Just make sure not to be obnoxious and go all out on a sample-collecting frenzy if you're not honestly considering buying something - it's just rude and inconsiderate to the sales associates. By the way, I won this Essie nail polish in Day Without Blues on the TOMS Facebook page :)
Gifts:: It's kind of cheating, I know. Especially when they live in a completely different state and you actually gave them your address so that they could send it to you, all the while knowing you shouldn't be allowed to acquire any new makeup. All I can say is that it's rude to not accept gifts, right? ;) I'm just kidding, by the way - in no way am I suggesting or asking that anyone send me gifts.
Mascara:: I hadn't really thought P10P all the way through before embarking on it, and when I found myself mascara-less a mere 3 weeks in after my mascara dried out, I panicked...and after I was done panicking, I bought a new mascara. To be fair, I bought a simple drugstore one that costed $5, not YSL Faux Cils or anything. And let's be honest, P10P is cool and all, but no one wants to look fugly doing it.
Lip Balm:: By far one of the easiest and quickest things to use up, especially if you have dry lips like mine. Just keep slapping it on like nobody's business and you're bound to finish one up in no time.
Minis:: You know those mini Lipglasses and Lustreglasses that MAC releases sometimes around holiday time? Well, they have 0.08oz compared to 0.17oz in full-sized versions, BUT a full-sized Dazzleglass only contains 0.06oz and a full-sized Cremesheen Glass contains 0.09oz, so technically, the minis are not really all that mini after all, and are fair-game for being used up (hopefully at a much faster rate) and counting as 1 product each :) I learned this fun fact after reading a post on Sandra's blog a long time ago!
As you can see, some of these are loopholes; others are bending of the rules/cheats that I've attempted to mask as 'loopholes'. I hope this helps some of you who are contemplating embarking on your own P10P! We can do it!