We haven't walked the Primitivo yet either but I kept track of the weather along the route early last May and decided to bring a sleeping bag rated at 0. I use a compression bag to squeeze it down, not to fit in my 45 l pack, but so that I can make my pack more compact. I have a 45 l, because when I tried packs on, it was the most comfortable. I'm also bringing tights that can second as long johns and will sleep in them if I'm cool. The weather may be warm but spring is always unpredictable.
We will be just behind you. We will start walking the afternoon of the 3rd or on the 4th, late morning.
Hi Anna -- I thought it might help you on the pack decision if I posted my packing list for my 33 L pack -- you can compare and see if you have more/bigger stuff! Hope this helps. This list is from skin out so it includes every single thing! It totals 17.1 lbs or 7.7 kilos. I calculated what will likely be inside my pack and that comes to 12.19 lbs or 5.53 kilos. I hope you find it helpful.
Liz
Outerwear
Osprey Kestral men's small Backpack 42 oz
REI Rainwall Pants 9 oz
North Face Venture Waterproof jacket w/ pit zips 11.3 oz
Fleece Vest Homemade PolarTech 100 8.5 oz
Marmot rain/sun Hat 2.7 oz
Manzella convertible running gloves 1.4 oz
Merrill Moab hiking shoes 29 oz
New Balance Minimus trainers 8 oz
REI Trekking Poles 15.5 oz
Dirty Girl Gaiters 1 oz
Sleeping/ Eating/ Drinking
Platypus Water system for backpack 5.4 oz
Sea to Summit Traveler TrI Sleeping Bag 13.7 oz
Sea to Summit Aeros Ultralight Inflatable Pillow 1.5 oz
spork 0.6 oz
cup 1.3 oz
Ear plugs (2 pair) 0.3 oz
sleeping eye mask 0.9 oz
Clothes
2 REI short ankle socks 3.2 oz
2 feetures regular socks 4 oz
1 Lands End long sleeve turtleneck base layer shirt 5 oz
2 Patagonia cami-bras quick dry 6.4 oz
3 Ex Officio underpants quick dry 3 oz
1 Lolë quick dry sleeveless top 4.8 oz
1 Lolë quick dry short sleeve top 6 oz
1 Montbell OD Shorts 5.1 oz
1 pRana roll up stretch convertible pants 10 oz
1 Long sleeve button wind/sun vented shirt (homemade) 4 oz
1 pair soft draw-string gym shorts (for sleeping) 4.3 oz
1 Montbell Zeo-line light weight long john/tights 4.1 oz
Sunglasses & protective cover 1.5 oz
Bandana 1 oz
Toiletries & Laundry
Packlite Ultra light camp towel 1.8 oz
1 Dr. Bronners Soap Bar (person, hair, laundry) 4.6 oz
Soap Case 1 oz
small hair brush 1.9 oz
small toothpaste 2.5 oz
toothbrush w/cover 0.9 oz
small deoderant 2.5 oz
spf 50 lip balm 1 oz
sunscreen/lotion 4 oz
razor 0.8 oz
Sink stopper 2 oz
8 small clothes pins 1.2 oz
shower shoes 3 oz
Miscellaneous
sea to summit ultra light stuffable daypack 2.4 oz
1 small LED flashlight 2 oz
1 homemade 1st Camino stuff bag (for electronics & misc small stuff) 0.6 oz
1 Sea to Summit ultra sil medium stuff sacks (for clothes) 0.45 oz
1 sea to Summit ultra sil small stuff sack (for toiletries) 0.3 oz
Pilgrim Credential + small journal 3 oz
Technology
iPad mini 7.5 oz
Logitech ultralight keyboard/cover 4.5 oz
tech cords: camera card reader, keyboard cord, ipad cord 1.4 oz
iPad/Keyboard neoprene protective case 1.3 oz
camera & small neoprene protective carrying case 7.1 oz