The combination of Snugpak jungle bag and Special Forces bivvy bag works well till perhaps 8*C, with merino base layers probably till 5*C.
The Jungle bag is very light and compact, down bags usually aren't lighter or more compact.
But the cut of the Jungle bag is made for temperatures between 10*C and 25*C. Air can float around in it, if you don't close it totally.
Instead of the Jerven bag you could use a Defcon 5 Poncho, 400g, 50€, original Italian army stuff.
A good cheap light pot is the Tomshoo 750ml pot:
https://www.tomshoo.com/p-y6549.html
Of course the cheapest and lightest stuff is the equipment that stays in the shop.
I wouldn't take an emergency blanket with me, and no car windscreen thing. I find that is idiotic stuff, if carried additional to bivvy bag and insolation mat.
A Victorinox Compact is all you need for hiking. Even the ultralight Opinel Carbone No7 is enough for a week end.
Have a look to 1 litre Volvic wide mouth bottles in the super market.
Bic mini lighter.
Beer can stove videos you will find in the internet. To make them costs you 1€ and fife minutes work.
A beer can stove weights only 10g.
Prosecco aluminium cans with a smaller diameter fit better to small pots until 1 litre volume. Don't take iron cans, which are marked with FE, aluminium is marked with AL and not magnetic. Only spiritus stoves made from aluminium cans work well.
Aluminium foil from a cake or fish package gives a good ultra light windscreen. It's lighter than the fuel it saves.
A 30x40cm microfibre cloth from Lidl can replace a larger towel. Just wring it out, when it's whet and continue drying yourself!
You can dry toothpaste to little tabs and store them in a small zipp lock bag from a jewellery shop.
One way orange Wilkinson razors are light but tough. A folding tooth brush would be my choice.
Original Toppits Zipplock freezer bags are surprisingly tough, they are offered in 1 and 3 litre sizes.
Currently we discuss a Swedish army 25 (or 30?) litres ruck sack without frame in this forum, which is currently offered for 15€.
I guess it is very light, perhaps we will get the information about the weight later.
The original german army mountain troop rucksack in Cordura, 34 Litres, weights only 775g and costs used between 25 and 30€.
With only 510g this 30 litres ruck sack from Decathlon is very light and cheap.
https://www.decathlon.co.uk/arpenaz-30l-hiking-backpack-dark-green-grey-id_8332414.html
The Solognac 50 litres hunting ruck sack with only 1kg would be a bigger light and cheap option. A bit to large for a week end perhaps.
The Decathlon Rain Cut jacket is very light and cheap and waterproof enough if you carry additional the Defcon 5 poncho.
Decathlon offers a cheap down bag I don't own. 800 cuin down for this price is outstanding cheap.
https://www.decathlon.co.uk/sleeping-bag-trek-900-10-feath-id_8492707.html
I do not use down bags. Snugpack sleeping bags with plastic filling are nearly as light and compact as down bags and I can wash them in the washing mashine and don't have to care to much for them. In my opinion they are the better option for Britain, France or Germany.
