If your bus has all drum brakes, don't expect to come to a s creeching hault, especiallly if you have a load in your bus. The bus is heavy and when you add a load it makes it that much heavier and stopping is somewhat impaired. I'm not saying it's not possible, as In_Tow mentioned, Woogie did a nice little skid when I had to apply the brakes quickly the other day. But he didn't just stop, I had to really push down on that brake pedal, I thought I was going to brake it. (Get it? Brake it?)

A lot I guess, will depend on your load and how well your brakes are adjusted. Adjustment is a key factor as well. If your brakes aren't adjusted properly then not-so-good things can happen.
Your hand brake is both an E-brake and a parking brake, at least I've used mine as both. Will it lock up your back brakes and bring you to a screeching hault? Again, how well are your brakes adjusted?
Distance is my "best friend". I always pump my brakes before aproaching any stop. People don't realize when you pull in front of a 37 year old bus, your putting yourself, and others in danger. Since, I do realized this, I keep my distance. But there are occassion where I have still had to brake hard.
Don't fret too much over this. Just keep some distance, know your load, pump your brakes to slow you before a stop, and keep those brakes adjusted.
If you want, try a few panic stops in your bus and get know what your bus will or won't do in that type of situation.
I hope this helps some.
Take care and have fun!!!