As far as shavings go, you will have to have enough to bed the stall down initially and then more to replace the dirty bedding. How many bags you will require will depend on the base of the stall and how deeply you like to bed. On grass or dirt, you can use fewer bags because the ground will soften as the horse moves around in the stall. On cement or asphalt, you will need to bed more deeply in order to create a base and prevent scrapes.
My general rule of thumb for packing or ordering shavings is about four bags per stall to begin with. I will usually put three bags in each stall and then make a decision a few hours later about whether to add another (depending on the base of the stall and the size/fluffiness of those bags of shavings). I usually estimate that I'll need to add in another third to half of a bag to each stall each day after mucking out.
As far as hay goes, it will depend on the size and quality of the bales, as well as how easy or difficult your horse is to keep. I find that estimating about 3/4 of a bale per horse per day works quite well, but it's best if you keep track of how much you use at home and then bring a bit more than that, just in case. One of the most convenient aspects of ordering from the show is that you can underestimate the amount and then just order more later!