1. Kid. Applies to anybody substantially younger than me: my sibling, the dog, Sputnik, the chickens. Almost always appears in a greeting phrase such as "Hiya, kid." Occasionally I go a little Arlo Guthrie or Foghorn Leghorn with it, which expands the range of usage a bit, but normally I use it on things that don't quite have an independent existence... which is why my sibling doesn't like it.
2. Hon. Used before requests, or before questions that are probably going to be followed up by requests. "Hon? Could you go get me another one of these in a size large?" "Hon? Did you take the trash out?" "Hon, have you seen my brush?"
3. Sweetheart. Used before, or occasionally instead of, phrases equivalent to "You sure did that wrong," or "You are about to do that wrong." I noticed this was what I was using it for when I started calling some movie characters sweetheart without thinking about it: "Oh, sweetheart, don't do that!" Also used as an expression of sympathy (I use hon this way occasionally, too); you can tell the difference because if it's the sympathy one then there's probably a hug or a sad face or maybe an "I'm so sorry," attached. The tone of voice is exactly the same, because it's not a censorious sort of "doing it wrong," it's a kind of wincingly sympathetic "this is about to go / has just gone badly." If I use a string of probably-goofy endearments together ("Baby pumpkin sweetie-pie...") that's equivalent to "sweetheart" in that it is about to be followed by a carefully-phrased explanation of What You Just Did and How Not To Do It Again.
Also I use "sweetie" with reasonable frequency and "babe" now and then, but they do not have any particular secret auxiliary meanings that I am aware of.