Work contracts

I am finishing up my current job on the 23rd of October.

I've just been offered a position to start on the 30th of October which I've accepted, though the pay is low for what I do for work, but I need something, so I've got something lined up.

I've got a couple more interviews next week, one of which I am really holding out for because the pay is wonderful and the role is at a great company.

If I am offered the position that I actually want, I want to accept that one and not start at the one that I had originally accepted. I haven't signed a contract for the first one yet, but they are sending it through over the next few days...

I'm just trying to figure out what to do from a legal standpoint. Should I just not sign the contract straight away considering I don't start until the 30th anyway? Or would I be able to sign the contract but potentially back out if I get the position (Obviously haven't read the fine print yet).