"because a mage duel is supposed to be a contest of spells between two mages, using a magic item to directly attack an opponent violates the intent of the mage duel"
since it's supposed to be spells only, i'd say weapons are out.
although that same paragraph mentions something interesting, "using an item...(anything that wouldn't end an
invisiblity spell) does not disqualify a participant."
so you could use a scroll, or any other magic item as long as it doesn't 'target' your opponent.
(you could also turn yourself invisible during the duel.)
as an 8th level caster, you should consider having a haste handy, if you have it. i'd cast it during the preparation because two spells and a possible counter spell each round will burn through your spells fairly quickly (so the duel won't last long anyway). if you're concerned about having any buffs dispeled, have your own dispel ready to use as a direct counterspell (automatic negation)
if you have silent spell and were invisible, your opponent couldn't possibly counter your spells. if you try this, remember: cast then move, always cast then move.
you should also consider a first round summoning. just something to get in your opponent's face. of the summon monster IV creatures (the best for a duel, IMHO):
(flyers) 1) arrowhawk - 1 attack per round, but it's a ranged touch attack for 2d6 damage
2) giant eagle - 3 attacks/round, more hit points than the arrowhawk, and better than the giant owl in this situation because it has evasion
(ground pounders) 1) thoqqua - good chance of setting your opponent on fire. fun for the whole family!
2) celestial lion - 3 attacks plus pounce, grab and rake, with some energy resistances (and smite evil, if your opponent's evil)
(honorable mention) imp - natural invisibilty and poison, nice!
ok, enough rambling...any other info you want to give on your PC?