If you're going to lose $145 for not spending it, you might as well buy the guards from the dealer.

Definitely get the FSMs for your cars. I haven't checked the price, but I imagine that the R-class manual is somewhat expensive. If you're looking to also buy special tools, those that apply to your car are listed in the manual.

How about maintenance items that you know you'll need in the future? Oil, filters, anti-freeze, etc.