If you go to ice trolls with a cannon then take prayer pots if you're below lv 100 or less than 70 defence. I personally go to the trolls in the tunnel of the entrance to Keldagrim, not a very good spot but they dont range.
On fire giants, knives are a lot better, another option against them is magic short and steel arrows. But out of knives and darts knives are a lot better on fire giants
This is pretty old, I'm not sure if its still profit now but when i was getting my magic up I alched addy plates and rune legs sometimes give profit depending on the market. a reminder this was a while ago.