Oh you actually use the stack? I'm surprised you don't just put all the tickets in a heap. I can give you some pointers on how to do that if you'd like.

I find that when a user continually makes a stink to get their ticket dealt with first, I gently try to correct them, and when that inevitably doesn't sink in, and they call during a critical issue, I tell them quite firmly that things are down and nobody at x site can work, so your printer will have to wait. Log a ticket and I'll address it when I'm done Brenda.

.... They usually back off when you make it clear to them that they're not the most important thing you're dealing with at any given moment.