Hmmm...are you looking to be useful or are you looking to score well?
Seriously - if you're looking to score well, then make your entries things which could also have been conceivably entered in one of the other categories. I've seen people donate software templates and computers for kingdom use, and no matter how useful they may be, the judges seem to have trouble scoring those items fairly. I don't blame them, mind you, since every other category has the question of "how well made is this?", and especially in the case of a donated computer, it's much harder to adjudicate whether the entrant did well putting it together - that'd require a whole set of expertise that isn't normally called upon in Amtgard. But if your score matters to you, then stay away from such stuff no matter how badly needed you think it is. Make those kinds of donations "off-camera" and don't risk dragging down your average score because you put the judges in a bad spot.
On the other hand, *because* utility is a criterion in the Rose category, this is one place where Quantity *can* be every bit as important as Quality. One hand-made and hand-tooled leather belt is lovely and wonderful...but it only benefits one person. A half-dozen matching tabards may not be quite as impressive-looking, but it has a greater impact on the game because that benefits six people that might otherwise be running around in T-shirts.
IMO, if you've got the chops for it, lendable garb is one of the most valuable contributions you can make, because the garb is what sets us apart visually as Amtgard as opposed to a bunch of hoodlums in the park. Garb gets us attention, which we can occasionally leverage into recruiting opportunities.
Lendable weapons are a close second, because so much of this game is melee combat, but for the love of gods don't enter them. Unless things have changed radically in the three or four years since I took A&S seriously, weapons never score worth squat.
After that would be things like sashes and spellballs. Especially so if you have a lot of new players, because then they can try out a few different classes and see what appeals to them. I was a freak of nature for jumping straight into the Healer class my first day and never wanting to be anything else.
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"And in the end, we decide if we're remembered for what happened to us or for what we did with it."
~ R. K. Milholland