The ring by the tree is at the inn. It is a bitch and a half to find, but worth it. There is also a great set of armor at the edge of a field in Nashkel.
The pantaloons are an enigma. Though having them at the end of the first game will cause them to appear in the second. There are other pantaloons, and having them can be of great benifit to your unit (is there a pun there, or perhaps a hint, I don't know). :D
The pantaloons are indeed an enigma. Never leave behind the pantaloons!
There are quests in Shadows of Amn and Throne of Bhaal to get two similar items, which can then be combined for a nice late game item - it’s not overpowering by the time you get it, but it is very handy. You will also get a Randy Johnson suit - and yes, I’m being purposely enigmatic myself.
Some simple tactics (or exploits if you wish) that can make even the hardest battles relatively easy…
“Stinking Cloud” can be cast at the edge of the “fog of war” and will envelop off-screen enemies, neutralizing almost any enemy mage. You can then walk up and pummel enemies with arrows and distance spells.
“Summon Monster” can be cast similarly. Enemies will fixate on the summoned critters, giving you precious time to take out a few enemies.
“Cause Fear” will easily turn the tide of a battle if you are able to get a few enemies to turn yellow and flee.
Once Imoen gets Boot of Speed, she can sneak, backstab, and run with impunity.
There is a Ring of Wizardry hidden early on the map in a hotspot only a couple of pixels wide. It is a huge help.