Hey man, this is HTW from the sounds page.. I use a different name here.
First of all decide what the odds for getting a prize should be. Let's say you want a heart 20% of the time, a rupee 20%, 5 rupees 10%, and nothing 50%.
When the pot is destroyed, get a random number between 0 and 100 (or more precisely, 0 and 99.999). If it's 0 to 19.999, spawn a heart, 20 to 39.999, spawn a rupee, and so on.
So put this in the pot's Destroy event:
var rnd;
rnd = random(100);
if rnd<20 { instance_create(x,y,objHeart) }
else if rnd<40 { instance_create(x,y,objRupee) }
else if rnd<50 { instance_create(x,y,objRupee5) }
And to show the smashing, make a new object with the smashing animation as its sprite, and instance_create() it just after that code above in the same event. Give this new smashing object an Animation End event, and in that, the object destroys itself.
I wrote a more complicated example, if you want the odds for prizes to change during gameplay. For instance if you get a Bow, you'll want the prizes to then include arrows. If that interests you, it's here:
http://www.zfgc.com/index.php?topic=13011.0