Bondo is a brand name of a body filler, just like Colgate or Closeup for toothpaste. They call it bondo because it's very common in US, just like how Filipinos call toothpaste as kolgeyt, lol.
I personally use Bronco bodyfiller, but sometimes I use Polytuff. Most car repair shops here in Laguna use Polytuff bodyfiller for fiberglass filling, so it's up to you to choose.
You can buy Bronco and Polytuff from Ace Hardware/Handyman. They also sell plastic body filler applicators which comes in pairs. Just cut the 2nd pair to different sizes, so you'll have a wide variety.