I don't see any explicit rules in when or how to use option cards. The rules on page 8 talk of option card priority and refer to using 'an option card'. Can I use two at the same time, such as Ramming Gear (which doesn damage to the pushee) and Reverse Gear (which alters how far you back up)?
Yes, as long as they don't conflict. (For example, you couldn't use the Mini Howitzer and the Tractor Beam at the same time.) There's nothing in the rules that says otherwise. There are a few places that do mention having more than one option card; surely they'd have mentioned if you couldn't actually use both.