Learn to say no -- and ditch the guilt
Now that you've got your to-do list sorted and off-loaded some of those jobs onto other willing people, it's time to remember that you are absolutely, positively unable to add anything else to your already jam-packed schedule.
It's a busy time of year, and people are going to ask you to do things - in fact, people are going to try to offload some of their tasks on to you, just as you have done to others. There's nothing wrong with this - after all, we're all trying to make things easier for ourselves so that we can enjoy the holidays without wanting to scream (or drown our sorrows in a litre of cheap booze-in-a-box). But when you're already so busy you can't possibly take on any more, you need to learn to say no.
It sounds hard and for many of us, it is - especially when people phrase their requests so nicely. "Grandma would be so happy if you'd make a family album with all the kids' photos in it for her present!" is awfully hard to resist.
Likewise, commands are difficult to argue with - "I'll need you to pick up a punch bowl from the party hire place for me" doesn't invite any discussion, and often leaves us seething with resentment after someone has talked to us this way.
Instead of resigning yourself to taking on one more job or responsibility for someone else, exit gracefully. Frame your "no" with two positives - say something like, "What a good idea for Grandma's present! I've already got her something, but that sounds like a neat gift for her birthday." Telling the truth also works: "I wish I could help, but I'm flat out right now. Maybe next year!" Or find a reasonable compromise: "I won't have time to make dessert, but I can pick up a cake from the bakery on the way!" (or better yet, "I can order a cake from the bakery if you can pick it up!").