It is really quite simple, unless you are having to do major foot repair, you should never be at an aid station for more than 90 seconds. DNF’s happen at aid stations because they are inviting, relaxing, and comfortable. They are filled with people who will listen to your complaints and give you anything you want while you sit there. The longer you sit, the harder it is to get up and move again. So to prevent this, you want to try very hard to keep your aid station duration under 90 seconds, which is easier than you think. DNF's at mile 92 have happened at 100 mile national championships (the people in the top 5) because people sit too long and cramp up physically and give up mentally. You can avoid both by spending as little time as possible at the aid stations. It's not as hard as you think..
This "go fast at aid stations" mentality is not just for people who are trying to get fast finish times, it is about keeping moving. It doesn't matter if you are at the death march stage of the race, you still want to get in and out of aid stations as quick as possible. Once death march comes along, you are going to want to sit and relax for a while. And THAT is how most DNFs starts.
#1. Don't Sit
Your body wants to stop, it will want to stop after you have done 10 miles. Sitting is what your body wants to do, then lie down, then sleep. You can sleep when you cross the finish line. Only if you are changing shoes do you want to be sitting. Of course you are tired. Tough. Suck it up, buttercup.
#2 Prepare Mentally Before You Arrive
You will have plenty of time before the aid station to think about what you want. You want to keep your mind frosty during the run anyways, so always being keeping a mental list of stuff you want to do when you get to the next aid station. Are your socks wet and need to be changed? Need a higher concentration of liquid in your handheld? More sunscreen sprayed on you? What pills are you going to take? Whatever. You should not be waiting until someone asks you about your feet to know if you need to do something with your feet.
#3 Make Sure Your Crew Knows Your Plan
Your crew (properly prepared) should be kicking your butt to get back on the course. No excuses, no whining allowed. Get your stuff, change what needs to be changed and go. You can chat when you cross the finish line.
They should know what you need, pills, new socks, etc. They should know your drop bag contents better than you. They should not have any sympathy. They should be heartless. If they have a stopwatch, have them time you when you get there, giving you a 90 second countdown. They should be pushing you to get out. You want your crew to be cruel. Get it? Crew-L? I crack myself up sometimes…
#4 No Story Telling
There will be plenty of time at the finish to tell your crew all the fun stuff that happened. Don't waste breath in the aid station telling your story. You are allowed to say "Remind me to tell you later about the crocodile I stepped on 2 miles ago".
#5 Prepare Your Gear for the Aid Station
You are going to have your handheld refilled at the aid station. Was it water and now you want soda? If so, open the top and dump it out. You can do that while you are running, don't waste time having the aid station worker unscrew it. You want to be handing them an empty bottle with the top off and saying 'soda, please' and that's it. Are you changing out your shirt or changing your hat? Get the old one off, it will save a little time, but more importantly, will prevent you from forgetting during that precious 90 seconds.
#6 Know Your Drop Bag
You have your bag packed with all the stuff you will need. Know what is where, and make sure your crew knows too. The last thing you want is spending 60 seconds trying to find that small tube of whatever. 1 gallon clear plastic bags with logical groups of stuff is good. For example, all your bottles of various pills in one bag. 3 pairs of spare socks in another. If your crew can do it, it's best if your entire drop bag contents could be spilled out on the ground before you get there so you can quickly find what you want.
Get in, get out, keep moving.