Coming in at number 4 on the list.
It’s actually hard to separate the items at this level of the list but this one wins the spot based on multiple uses and compact size.
Learnings of multi tool/pocketknives
Multi tools with pliers built in are less useful than you think. you would be better of with an actual set of pliers of that size once you consider cost and strength of the pliers.Certainly some situations require pliers but if you really need pliers you might as well get vice grips which are self locking pliers.
Compare the cost of multi tool with pliers versus a good pocket knife and a good set of vice grips.
So we have narrowed it back done to pocket knifes really.
Knife: the blade must lock and be very sturdy when locked. A knife will allow you to modify and construct many things.
Screwdriver: Phillips (+) and flat head (-). very few tools can improvise the screwdriver well.
Leather needle: allows some really versatile sewing with thick fabrics and threads. imagine sewing para cord through thick vinyl.
Saw: being able to make a straight cut is great for making things from branch size wood. much faster and safer then hacking with straight blade.
Nice to have:
Fish scaler: for obvious reasons.
Bottle/can opener: these are only really useful if there are bottles and cans around.
Bit driver: you need the bits and the uses are somewhat limited.
Propane torch: I saw these additions years ago, great for wet wood, nice but shouldn’t rely on it.
USB key: Most of the ones i have seen were very small in capacity.
Fork: Nice idea but are you really gonna eat off it?
Parcel hook: Carrying a parcel wrapped in string is not useful.
It’s easy to buy a knife/tool with lots of extra attachments which will only make the tool heavier bulkier and more unwieldy to use.
Be prepared to spend on this item as it’s a solution for so many problems and it’s one of few hand tools you will be likely to have. Stick to major brand names that have a reputation for quality. Check the legality of carrying knives where you live. In some cases you can claim you are carrying a knife for cutting up apples (because that how you like them) in case you need a reason for carrying one. if there is a way of attaching a key ring or similar item try to find and attach a glow in the dark key ring to the knife. it well help you to find it if you put it down in the dark.
In terms of size, be looking at a blade length of about 75mm-125mm.
Cost: you should be looking around the $100 mark