I just read the manual and it said magical benefits do not stack, so equipping a ring of protection and +1 armor do not give +2 AC. Does this also apply to weapons, namely ranged weapons like bows? Is there any benefit equipping + 1 or higher bows with +1 or other magic arrow types (arrows of ice for example)?
Not sure if this helps at all, but there are stacking (sort of) bonuses with melee weapons when equipping something like the Gauntlets of Ogre Strength on a weaker-than-18/00 character and a +1/2/3 weapon. They aren't the same exact style or source of bonus, but the extra THAC0 and damage of the gloves (a result of the strength boost) piles on to the weapon bonus(es).
There is also a pair of bracers/gauntlets (weapon specialization something or other ?) you can get that provides bonuses to both THAC0 and damage, IIRC. And while the description reads melee weapons only, it seems to apply to missile weapons as well. The dude on the far eastern edge of one of the far eastern parts of the world map has them. Can't recall his name, but he's east of the Firewine Bridge area. I have also gotten an extra set of these when I first met and was attacked by Tazok. I ran circles around him, while I was hasted, drilling him from afar with arrows, before he could talk to me the 2nd time and end the encounter.