Duct Tape is an ABSOLUTE must for your kits. There will always at some time or other be a need where something has to be fixed, or held in place and that duct tape fits the bill.
Get decent quality tape as well, because otherwise you may regret it. Some cheaper duct tape doesn't last as long, or simply doesn't stick enough. You don't want to wound up talking to yourself if you know what I mean because you cheaped out on the quality when you need it.
I have used duct tape for many different things, such as shelter building, boot repair, first aid, making a sleeping bag with Heatsheets from AMK, making grommets and I am sure other things. I am certain that without the duct tape at one time, and with plastic drop sheets at other times that I would have had to rethink my shelter designs and in turn would have made it harder to protect myself from the elements. If you go for only one or two nights that is one thing, but when you go out for weeks it is another.
It can be used for clothing repair as well. It also contains petroleum based ingredients so can be used as tinder if need be.
I repeat, Duct Tape is an ABSOLUTE must for your kits. Do not leave home with your kit without it. I'll add that having a 9' x 12' plastic dropsheet can dramatically increase the protective value of your shelter. On the right you can see a foot, well, that is my right foot that needed to be tended to during a hiking trip. If I wouldn't have done that, I most probably wouldn't have finished as planned. During that trip, I had seen two men that were camped at the same site I was at, that had two small tents on one wooden platform designed for one tent.
The real problem occurred when it had rained a lot and they weren't able to stretch their rain flies properly and as a result during the night their gear got all wet as the water went through the flies which were touching their tents. In the morning they had broken up camp at the same time as myself, and it was raining as we were doing this. It had rained more than usual for that time of year and I was concerned during the first 6 days of the trip for my gear and I getting too wet and having to quit to avoid hypothermia.
Anyhow, to get back to what happened, I'll tell you. I learned about their problems afterwards when I had seen two men coming back on the trail at some point. It was the same two that were at the camp with me. We had each minded our business at the camp so I didn't immediately recognize them. We spoke as they crossed a stream I was going to cross, and mentioned what had happened to their gear. Their trip was ruined and it would have been a dangerous trek out. This trail was challenging for certain reasons.
All it would have taken is a $1.00 CAD (in 2008, now $1.50) 9' x 12' plastic sheet to cover both their tents and their trip would have been saved. They also should have considered having organized their trip to use two separate platforms. Anyhow, for a buck or so all of this trouble could have been avoided! DO NOT underestimate the importance of having a modern method whether it be a tarp, tent or other to shelter yourself from the elements as well as to know how to use your equipment properly!
This is why I, as well as other people who teach about kits say that you need to know how to use what is in your kits. You may have a tent, but if you do not set it up correctly as the men above, well it is almost as though you had no tent. All their gear was wet and they couldn't bear another night in their cold and wet sleeping bags. This is EXTREMELY important to understand. It could just as well be a fire you are attempting to make but don't know how to use a firesteel, or it could be something else.
Out in the woods it isn't time to mess around when your decisions count, just like it isn't time to learn how to swim when the boat is sinking. Practice time is the time to make the mistakes, so that you can avoid them under more 'real' conditions. Mistakes will inevitable be made, but understand that you put the odds in your favor to reduce them through prior learning and practice. Some errors are more easy to avoid than others, just like for the tent problems above. Get yourself trained in the techniques that can help protect you.
Below are some links on duct tape and its uses. Just don't go nuts with the stuff! I saw climbing rope as a use for duct tape, very dumb so buyer beware. The link descriptions were taken from Google.
Don't Forget the Duct Tape: Tips & Tricks for Repairing & Maintaining Outdoor & Travel Gear (Don't Series)
By Kristin Hostetter Paperback 4.0 out of 5 stars ...
Duct Tape Everything. Here you'll find duct tape information, duct tape fashions, duct tape scholarship information, duct tape instructions, duct tape ...
101 Uses for Duct Tape. "Duct tape is like the force: It has a dark side and a light side and it holds the universe together." - Carl Zwanzig. Credit goes to the list ...
Get the WD-40 as well, many uses for it. Here is a link to the manufacturers website for more info. Be certain to have a look at their Disclaimer while there.
Duct Tape – Wikipedia
Duct tape, or duck tape, is cloth or scrim backed pressure sensitive tape often sealed with polyethylene. It is very similar to gaffer tape which was ...
Duct Tape vs. Duck Tape - an explanation
The first name for Duct Tape was DUCK. During World War II the U.S. Military needed a waterproof tape to keep the moisture out of ammunition cases. ...