Interesting there are two nature preserves there. Any special reason ( plant or animal) why?
Western reserve can be translated as "Bird's Paradise". Due to some special conditions (Im not a specialist in terminology to be honest) there are rare water and mud bird species stopping there during migrations. Over 200 species to be seen. Eastern one is called "Seagull's Sandbank". Its the only place in Poland where Sandwich tern is breeding.
So with a bit of additional research, I polished the list to full completion. Of course there will be tons of changes after some terrain tests, but for my first spring hikes it came out like that (in order, I would throw away the last thing first and so on):
Essentials - not going anywhere without these:
1. Knife (Helle Gaupe)
2. Firesteel (Solo Scientific Aurora)
3. Backpack (Karrimor 45 Sabre)
4. Sleeping bag (McKinley Laguna)
5. Foam mat (Plain)
6. Tarp (3x3m, DD Hammocks Superlight)
7. Paracord (30m)
8. First aid kit
9. Lunchbox (Zebra 14)
10. Compass (Silva Field)
11. Personal hygiene kit (Toothbrush, paste, soap)
Secondary - I could manage without, but they will make the trip much easier and/or safer:
12. Axe (Hultafors Classic Hunter)
13. Canteen (Wildo Hiker Bottle)
14. Whistle (Mil-Tec Bobby)
15. Sewing kit (BCB)
16. Additional clothing set
Additional - completely optional, but will be very useful for me personally:
17. Tinderbox (Light My Fire Tinderdust)
18. Notebook & pencil (Rite In The Rain)
19. Duct tape
+ Basic clothes, phone and supplies not listed as a kit part
Comes up to a total of 19 compact and lightweight items. Im very satisfied with this kit quality to price ratio. There will of course be changes (probably will add headlamp quickly, buy Osprey pack and Snugpak bag etc.) but I've already spent far to much time polishing that list. So enough planning, time to buy that stuff. Thank You very much for all help and advice. I will make another topic about clothing when I'll finish gathering the stuff listed above. Cheers and see You!