Every. single. time.
I have a few things that help keep me sane.
Spreadsheets: basically I have every single thing typed into a spreadsheet. A document or even a pad of paper with pen would work but I'm a spreadsheet gal. By having everything in writing I can easily add things as I go along so I know I won't forget that next thing that comes to mind. Each trip I start off using the spreadsheet from the previous trip so I have that as my base since I know it worked before. I
know I'm less likely to forget something this way. This gives me some confidence that at least nothing important is being overlooked. In addition, I can print out some of the checklists so I can see what's been crossed off and therefore also what's left to do. I do not cross anything off my packing list until it's actually in a suitcase or carryon even if I've got it nearby because that way I
know I haven't forgotten it.
backup plans: Things don't go as planned. They never do. Because of all the planning and research I've done I can turn to plan B. Plan B isn't nearly as detailed of a plan as plan A but it is still a plan. For example, when we've forgotten something, it's been very easy to just go buy a replacement. If a ride is closed then we just move on to the next ride and using a chart I've got of best times per attraction I can easily see if there's another good time I can fit in that attraction or I just accept that it's something we'll do next trip (there's always a next trip for us). If somebody's not feeling well then I know we can stay at the resort and get safe food from the food court and cancel an ADR if we have one. If luggage is lost then I at least know that I've got all of our medications and planning materials as well as a good supply of snacks in my carryon and everything else is replaceable. I make sure to pack at least 3 extra days of medications just in case there's some kind of major delay getting us home.
Basically, I take control over the things that I can. My anxiety is really all about lack of control.
I do make sure that our trips are pretty close to our at home routine so that one's not that big of a deal for me. I have to do this because of my autistic DD15. Yes it's very different wandering a park than it is being at home but the basics of the day are the same. We wake up and go to bed at our normal times (actually to bed a bit earlier at WDW because we're tired) and we eat at all of our normal times. It really does make a big difference.
I really don't have anything for the being away from home. At this point WDW is very familiar to us so this is nowhere near as anxiety causing as it used to be but there is still some element of that each trip, especially since we like to try new resorts every other trip. At least there's some sense of familiarity though.
I have the restaurant anxiety every outside of WDW but it's nowhere near as bad at WDW. Even with all of my great experiences I'll admit that there is some degree of this one though. Looking back over some of my past dining reviews and looking over the menus at the restaurants where we'll be eating help a lot. Having a list of foods that are easily found around the parks as well as places I know I can find them helps a lot too.
I start my grocery list at least a few weeks ahead of time and keep tweeking it until it stops really changing each time I look at it. I place the order maybe a week before the trip. Knowing I've got these groceries also helps with the previous restaurant anxiety as I know that we'll have some food in our room.
I'll be honest. The work one doesn't stress me. The trip we took this summer was actually a really bad time because we had a major implementation happening at work (govt agency changed dates on us last minute so implementation happened a couple weeks late or I would have been there) but I just left and didn't think twice. There are others who can cover my stuff. There's always some kind of deadline and something else will always come up.
I do make sure that I've got all my bills up to date and there there will be no payments for anything due when we're gone. I love online banking and the ability to schedule payments. I basically have things like this go into the checklist in my spreadsheet. That spreadsheet really does come in handy. Mail hold, checking on
amazon deliveries, etc all go on the spreadsheet. Seeing the items get checked off really eases the anxiety.
I sure do wish I had an answer for the travel anxiety. I always worry that my autistic DD is going to have some kind of meltdown with TSA. She did once really snap at an agent and I was sure we were going to get hauled off for some major additional screening. It didn't happen and we've always had nothing but great experiences but I still have that anxiety every single time. This is one area I can't control so it gets me every time.
My kids have learned to just tune me out if I feel the need to have a little chat with myself in the car, on the way to some activity of theirs. 
