If the rucksack is made to strap equipment onto the outside it's often the best solution. But although there is Molle / Pals everywhere nowadays it's rather unusual among professional users to strap stuff outside nowadays.
The German army for exampje did put more and more stuff from outside into the rucksack with every new issued rucksack model since more than 100 years. But otherwise they did haul the complete equipment less and less in the same time. The younger rucksacks are optimised for car transport, 100 years ago they were optimised for marching armies.
But also the back / carring systems became better and that's why the modern rucksacks are more comfortable to carry than the old models and new models that are meant to strap stuff outside are extremely rare. The Austrian RU 90 is one of the rare examples, but not really if you compare it for example with a swiss fur infantry rucksack 1898 which was in my opinion the most intelligent system to strap equipment outside that was ever created.
But well, that's museum stuff. Let's talk about your own equipment!
The advantage of the Karrimor SF Sabre 45 is the option to put the large side pouches onto a relatively small rucksack that still has a good back / carrying system which allows heavier loads how they come together in current trekking or bushcraft use. With the side pouches you reach approximately 65 litres total capacity what's optimal for 3 seasons use in most areas in Europe.
You can put into one side pouch a Pathfinder Bush Pot 64 oz / 1,8 litres so far I am informed or for sure an Austrian or Rumanian mess kit with flat bottom after German WW2 pattern, that works with a modern gas stove and can be used as rat proof food container during the night outside the rucksack. On top fits a modern field bottle of British, American or even French origin I think, together with cuttlery kit and fix blade knife. That means you have the complete kitchen in one side pouch. In the other you can put a tarp, rainsuit and second field bottle. What could get packed whet goes into the side pouches.
In the main compartment you carry a sleeping bag in its bivvy bag, a German army folding mat that's easily available in Britain as Multimat Adventure 4 XL, your self inflating sleeping pad and on top of that a 7 or 8 litres dry bag (Ortlieb PS10 or Snugpak) that contains your spare clothing and polyester fleece jacket and can be used as a pillow during the night. As you see your bed is seperated in the main compartment. That's very very practical!
In the lid pouch you put your head torch and tooth brush and you are ready to go if you didn't forget compass, map and toilet paper.
That is the currently most practical way to carry a 3 seasons lightweight equipment that's based on equipment that's made according to the Specifications of NATO armies, that means as durable as possible, cheap as chips and green as grass.
If you pack your stuff like that and don't go for camping below the freezing point that's surely all you need.
OK, that's no entire packing list. Cordage, cigarette lighter and a few other essentials you should add of course, but you surely got the idea.
