I have some info that can be useful for people trying to win the game solo.
Playing Solo Tips
In my last playthrough i had tested some good loot hotspots and found that they do not appear to be dependant on story progression.
One can just finish Ernie island solo and go straight to K16 fort and speak with the colonel there, this allows you to interact with intendants in the fort, one of those gives you PSG-1 sniper rifle with 100% garantee, second one gives you some good grenades and his room is full of crates with more.
Also if one has good intelligence, room with colonel contains decorative globe that can be opened to get AA-12 auto shotgun and some magasines, as well as several aniques that can be sold in Cacao later.
I suggest evading all encounters on the way and make a route H2 -> J8 -> I10 -> K12 -> K16. Where will be one fight on the way at abandoned factory at K14, which is another hotspot for good loot, you can savescum entry to this location to get one of the following: Steyr Aug, AKSU, AR-15, Minimi LMG, PSG-1, C4 explosives & remote dets, AA-12, good body armor and stuff like that. You can get this trip right when you get access to the sea and start usual progression through the game, but with PSG-1, Minimi, 40 mm greanades, good armor even before you take your first steps on the mainland…
Easiet way to get back is K18 -> K12 -> J11 -> D11 (bridge port) where you will have to clear like 10 enemies to get access to sea again and redeploy in Savanna at F9 to resume your normal game progression. I think this may be of great help.
When you liberate the outpost on Ernie, make sure you go in with recon data for the area. This will allow you to loot a crate near the top end of the ladder to minefield, containing sizeable amount of C4 exposive. When you get back to Ernie, if you have 50 explosive skill you can manufacture like 40~50 HE grenades for 40 mm grenade launcher attachment on your fav assault rifle. Do not underestimate those, they are very very strong and can be launched for great distances even without MGL with just simple rifle attachment. Having like 50 of those from the start can help immensly in the early game, or you can keep those for tougher situations and engagements later.