Conniemac, I understand how you feel. My boys are 17, 14, and my youngest will be 13 next month. All ds17 wants and needs is money so he can have the freedom to drive more and go out with friends. Ds14 usually has a bunch of money because there is nothing he can think of to spend it on. I too, feel like all the thoughts that go into shopping for those perfect gifts is part of the Christmas spirit. It's not the getting, but the giving and the love and thought that goes into the whole process. Even though money and gift cards or things they hand pick themselves are starting to become more likely for me too. I still plan on finding at least 1-3 smaller, less expensive gifts. I actually end up having to shop more, (rather than having to stop all shopping), keeping my eyes open all year for ideas. I do find that there are little things that they love. Ds 14 tends to really love different socks And quirkier things (he absolutely loves his dress socks with bananas on them), so I'm on the lookout for some fun/cool socks. I found a nozzle that sprays the soap on the car instead of needing a bucket for when ds17 washes his truck. I look for little things that maybe aren't' so common but not expensive either so they still have little surprises to open and I still get some of the feeling you get when you want to give gifts.
Since your kids have jobs, is it possible for everyone to participate in a white elephant type gift exchange for when you get back from your trip. You can set a very low $ limit. Then you will also get to still see the presents under the tree, and have some fun with your family opening gifts.
I think you should still put out your Christmas decorations, and put them up as early as possible so you can enjoy them. I think they really help with that Christmas spirit.
I think setting a shopping date with yourself for the angel trree, or the toy store for Toys for Tots, like Annie suggested would be fun. Make a day of it and go out to lunch. I think Ahorsesoul had an excellent suggestion of putting something under the tree for you too.