What particular sugar were you trying to get? Is it for priming or in your recipe,what style? If its priming sugar,dont even bother making a trip.If its a big belgian recipe that may be different but I personally probably wouldnt go out of my way for it, Id maybe try a good honey or light brown sugar or a good tasting sugar you like. A key to making a beer recipe the way its intended is sticking with the exact ingreadience although sometimes the outcome could be better or not as good as well,it just may be a little different and probably minor. Subbing a recipe certainly works but may get different results.
If your trying to boost the gravity,stick with more malt(dme or lme) with a small(or more) amount of hops. Those boosters or brewing sugar packs I think are dextros with a small amount of maltodextrin. It works but people seem to preferr malt extract,unless you want a little dryer thinner body with sugar depending how much you use.