Do you have some items on your list that you could do in a simpler way than you have in the past? I've always loved shopping -- I'd go out for a whole day just to look everywhere and collect gift ideas for everyone, then I'd go back out several times to make purchases. Now, I don't have the energy for all of that, but I really love being out in the stores and soaking in the very "Christmas-ness" of it! So what I do now is a shortened pre-shopping trip to the stores followed up by a lot of online purchasing, which is really easy now that I know what I want and where to get it.
If I can't buy what I want online, or I can get a better price locally, I only go to one store a day. If I need to do more or I'm getting multiple things, I bring my husband along and try to get a wheelchair so I don't exhaust myself completely. (Yes, at first it feels strange to be in the wheelchair, but I've learned to put that aside in order to conserve what little energy I have.)
Also, have simplified back-up plans for whatever you can. For example, I like to make pie crust from scratch. If it comes time to bake, however, and I just don't have the energy, I send my husband to the store to buy crusts for me so that I'll have both pies and my sanity.
