I completely for got what source I read this so I'll ask all, but wasn't there rules for wand, rods, or staffs to have multiple spells and still have 50 charges. Same activation rules and spell triggers rules with exception that the item charges are communal.
Wands cannot do this. Rods aren’t spell-trigger to begin with, though there is a rod of many wands in Complete Mage that allows you to insert multiple (separate) wands and use them at once (costing more charges than normal, and the charges aren’t shared). The only other spell-completion item I’m aware of are the scepters from Lost Empires of Faerûn, which can have either one or two spells.
The psionic analogues to staffs, psicrowns, also have this feature, but are power-trigger items.
The above is all true for Pathfinder as well as 3.5e, and largely true for 3e (3e psionics is wonky and I’m not sure about psicrowns there). I do not know about AD&D.