There have been some studies I've seen here and elsewhere (link) that adding citrus to green/white tea increases absorption of catechins.
In the past, I have used lemons or lemon juice to do this. The problem with the former is that it's messy and time consuming, the problem with the later is it can get expensive and they often have preservatives in them that are possibly harmful. I just found this product that I really like that has neither of these problems and is highly portable:
http://www.amazon.co...s/dp/B000HQR9J2
It's in a lot of supermarkets now (regular ones and maybe Whole Foods) and it's cheaper there than online. You'd be paying 8 to 11 cents a serving which is less than the 20 cents a serving I was getting from lemons or lemon juice.
Most importantly though, it tastes like real lemon (because it is) .
Here is the official website: http://www.truelemonstore.com/ --- Now that I look, there are also versions of the product in lime and orange. I haven't tried those but if the lemon is any indication it tastes like the real thing.