Just go for a "standard" kit you think that will cover you is BY FAR the easiest way to start. If you think you need further bits for any likely scenario - if you can do that from adding those other bits....
I've done this from a maintenance / checking / speccing side of things of "Aviation" First Aid Kits over a number of years - and it is a real pain in the @rse.... Anything from Weekly - to Annual - checks on the contents is tedious, and if you are trying to source individual bits that have a shelf life - you are much better off just tamper-proofing the new kit you buy - and then buying a whole new kit when the first lot of items comes up for expiry (IF you are bothered). Unless you are required by your Reg's to have something in particular - don't go overboard....
Depending on what you want (and where you are) a decent "Medium Leisure Kit" from St John's Ambulance (here in 'Straya) is about $75 (AUD), and to have someone you are paying to "check" it periodically is going to be vastly more expensive than a complete replacement every couple of years....
Just sayin'....