The tubes of Crystal Light have eliminated my need to repackage drink mixes. One tube containing, depending on the flavor, about 1 or 2 grams of product (I don't know what the packaging weighs, but it can't be much) makes a quart. There's a good selection of flavors now.
Another, bit heavier and more expensive, option is Emergen-C packets by Alacer. About 3 to 9 grams (again, without packaging and depending on flavor) makes only a 6-oz drink, but it's tasty and fizzy--a nice change of pace. The heavier versions of Emergen-C contain sugar--not much, though.