To “get some sugar” is to get romantic affection such as kisses, hugs, cuddling, and possibly even oral sex or intercourse. It means to get some of that sweet lovin’, that sweet stuff. A person with a romantic interest in you might come by your house with a different excuse but really they are trying to “get some sugar.” Or if someone was hanging out and then it unexpectedly turns romantic or sexual, you would say “Had I known I would be ‘getting some sugar’ I would have shaved.” To “get some sugar” denotes that there was some sort of romantic or sexual encounter happening that was a very good experience for you. Like tasting something sweet and delicious.
A coworker might ask you about a goofy smile on your face and you’d say, “Last night I went to my boyfriend/girlfriend’s house and was able to ‘get some sugar.’ Now I can’t stop thinking about it.”