"So tell me how will you resupply your water, food, fuel, how will an average family of say two adults and two kids carry, shelter, change of clothes, sleep system, food, water, weapon, spades/tools, medical kit, digging kit, coms, fire making and maintaining gear, pots for cooking and boiling water, water filter gear, lighting, spotting gear, hunting gear, and on and on."
[ I.M.O. ]
(If you have cache's & manage to recover any - then great. without caches & a Sherpa teams worth of supplies, then do not despair - read on)
The answer is pretty straight forward. You carry what you effectively can! The items must be prioritised in order for the situation at hand. If your carrying limit is reached, then the later items on the list can not be carried.
What you need to grasp is that the UK is a densely populated & built on piece of real estate. You will never be far from artificial shelter/buildings etc. Whatever you don't have or are unable to carry, then you must find it on the way or know the location where you have a good chance of getting it. You do not need to carry all the items you will need to survive. You can look for them on your travels.
Water is abundent in the UK. A water purifier & enough replacement filters is a far better idea than carrying a LOT of water. (carry some)
If it is a major event and you are forced to bug out, then you can forage for food in other dwellings/commercial/industrial/farm premises. Yes, there will be danger but it is a physical impossibility to manually carry enough food for long periods.
Fuel will be all around in abandoned vehicles on clogged up roads. If you are able to use a vehicle and the roads are clear, then you should have enough fuel to last a while as part of your preps anyway.
Sleep system - you mean a sleeping bag? & maybe a tent? Improve this by looking for empty buildings. Utility buildings are ideal as any workers are unlikely to show during or after a disaster event. This is where a crowbar or good quality hacksaw blades (or a lump hammer as advised recently by a friend) are useful to gain access.
For lighting, you will only need good waterproof wind up torches as you are unlikely to be carrying on with the usual up into the night civilized routines.
Only carry the tools you are likely to need and then consider weight. There are plenty of tools to be found in garages, workshops, retailers and industrial works if you need a special item later on.
Spotting gear - I take it you mean a spotting scope, then if you are with a vehicle, then this should be a good useful bit of kit to carry. If on foot, then the weight may be an issue. there are some v.small QUALITY monoculars available that fit in a v.small pocket easily. Usually 8x magnification, which is good enough. 20X is great, but is usually a full size scope for that. What about using a rifle/air rifle scope. These are slim & lightweight. If you put it in a compact waterproof padded case, then it will do the job just fine. Firemaking. Well, that is not a problem really.
Pots for cooking & boiling - Use lightweight nesting pots. Hunting gear? What are you going to hunt? along with all the other refugees? If your weapon is also your hunting tool, then you have it anyway. For hunting compactness, It is hard to beat a latex catapult with wrist strap reinforce. This are almost silent and will drop game at close range. Just a bit of practice is needed - like any weapon. It is small & light and ammo is easy to aquire. There are other options. Weapons can be heavy. Think what is practical & will also do the job. Can it be carried. Is it too overt or easily concealable when you don't want to stand out.. Can you keep it in ammo for long. How heavy is the ammo? Can you make your own ammo? Do you have the components for this and how heavy does that make the combined load? These are all serious questions for all of us. Presently I have a spring scale & I am weighing all my kit & severly modding it as necessary. Quite a few items have already been relegated to vehicle kit/BOB only.
Medical kit - yes is important, but how much & carriability is every preppers own conundrum.
Maintaining gear is simple. You will not be able to carry spares & materials for every eventuality. A small collection of sewing kit of HD needles/thread etc & quite a few leather rivets will patch most stuff back together. Gaffer tape etc & all the usuall suspects if you can manage it ok. Any specialised items may require a few key spares to be carried, but it all adds weight. Any kit you do carry needs to be designed so it is robust while not being unnecessarily heavy (of good thoughtout design), needs to perform the desired function adequately and if possible have multiple uses.
PSHTF, there should actually be a lot of equipment around due to our densely populated island. A quick mass die off will only exacerbate this. In fact the quick die off of unprepared dense populations is postulated to be advantageous to any survivors who make it through that initial manic period.
Carry what you can, forage for what you can't.
Trade & exchange may also be useful. If you look at what happened to the populations of the Western European countries in the aftermath of Hitlers demise, you will find it very unsettling reading. It gives some pointers on how the anarchy of society at the time played out. Try to imagine you & your family starting off from one of the problem areas and how that would dictate your limited set of options.
Happy bedtime readings, TL.