Unique experiences, not just vacations, are the best I've ever seen. If you can do those, you should be great. Make it personal.
I actually got this advice from an auctioneer and it really paid off. Here's a link with more info:
link
I can not stress the importance of having a professional auctioneer at your event. I believe 8-10 live items are all you need. If you are spending 3-4 minutes per item then your live auction should never go more than 30-45 minutes. You will lose guest interest and control of the room if it goes longer or gets out of control without a professional leading it. For school events it is important to make the event fun, uplifting, and to generate income. You want the parents to spread the word and come back next year. I have chaired our schools auction for 6 years. We have gone from $40,000 a year to well over $175,000 a year. My keys to success are 1) OPEN BAR for at least the first two hours during the silent auction, 2) A PROFESSIONAL AUCTIONEER will pay for itself in the long run, 3) A GREAT SOUND SYSTEM. The house sound system or cheesy sound system will end up costing you money, 4) NO LONG AND BORING SPEECHES. Your guests came to have fun and spend some money. A simple greeting and thank you are all you need. 5) FOCUS ON YOUR "FUND A NEED" portion of the event. A video or slideshow presentation pleading for a cause will help people to open up their wallets for your cause. It's better to spend your time on the "Fund A Need" portion rather than following up on a $10 movie ticket.
Good Luck!
I'm moving your question over to our Facebook page to see what community members there have to say about the number of auction items. I'll post a link here when the Facebook question goes live.