[Nerull]

Maybe I'm a bit of a stickler about soloing, but solo means solo. All the time (except for those few seconds where Imoen "invites" herself into your party). No pickpocketing the ring in that case.

However (SOME SPOILERS):

• Potions are your friends. Buy/loot them from any and all sources. JrKASperov is absolutely right about potions of defense and invulnerability, but you will need healing, booster potions, protection potions (clarity, etc.), and so on. These make up for your lack of magic.
• Patience is a virtue for a soloist. When you come across a group of creatures, use the fog of war to your advantage to lure 1-2 creatures out at a time. With no way to take down stuff like Protection from Magic Weapons, etc. you may need to trigger enemy mages' contingencies then run away and wait it out.
• Any items that summon creatures is an absolute priority. Staff of Air, Spider Figurine, Efreet Bottle, etc. are worth getting, and worth getting right away. The kensai is best as a flank attacker, and summons essentially give you a tank that distracts the enemy and allows you to attack without taking hits
• In Nalia's keep, there is the shield amulet. Get it, and use it. It essentially gives you scale mail AC, which considering the no armor restriction is a great find. Also, don't be afraid to sell it and buy it back to replenish charges.
• Consider taking proficiency slots in flails, especially if you are going to ToB. DoE is a great off-hand weapon to help anyone soak up damage, and FoA is actually a solid main weapon (crushing damage to handle clay golems, energy damage to soak through stoneskins, etc.).

Just some general pointers...