"Everything" is a common response. Unfortunately, these technologies were never meant to be used in such a fashion. They tend to be purpose built and only do one or two things. In effect, one implant can't do everything. And that's not sort of thing time and advancements will fix. Some of these technologies are just incompatible.
Keys are terrible--what are your options? That all depends on your situation.
Do you have an existing contactless access control system? If so, you'll need to identify the transponders that are compatible. If you administer the system (IE, can enroll a transponder), things are simple. You can try enrolling various transponders until you find one (or maybe more) that is compatible. The Dangerous Things Card Pack is great for this. If you do not administer the system, learn how to identify transponders. Once you know what technology it is, you'll be able to find out if it's clone-able. That link will also tell you the relevant implant (if any).
If you're looking for something to install now, we currently recommend the Viese. It works with the NExT, xMagic, xNT, xM1, flexNT, flexM1, flexM1 v2, and flexUG4. There is also a promising community project aimed at a retrofit option for UK style doors by forum members Chimpofm and DonFire.
If you've got a Tesla, you can use the Tesla Keycard App with an Apex Flex. Other than that, you're gonna need to do some work that will make your car easier to steal.