Unfortunately you can't use a mix of cash and contactless. We wish we had that technology but it isn't available yet. It would also slow down the whole boarding process. No one wants that!
With contactless, you can buy tickets up to £30 or £45 (depending on your area). This includes both paper and StagecoachSmart card tickets.
You'll have the £30 limit if you're travelling in these areas:
Areas with the £45 limit
Merseyside & South Lancs