If you are ready to do something straight away, without any preparations, you will do it at the drop of .... (what?)
a hat! (do something at the drop of a hat)
If you are tempted to spend some money, it burns a hole in your ... (where?)
pocket! (burn a hole in one's pocket)
If you are wearing very smart or fashionable clothes because they want people to notice them, you are dressed to ...?
kill! (be dressed to kill)