I'd also say something lighting wise.
As a beginner I hadn't appreciated how significant lighting could be, but I am rapidly coming to the conclusion that a lot of the best images I see on here and elsewhere are making very good use of lighting. I will certainly be spending on lighting - but not until I know and understand enough to make the right choices (plus I'm a tight git).
Even out walking, being able to manipulate the light on an interesting rock formation or plant or whatever would be very useful.
I suspect that if you felt that you needed a lens upgrade then you would already know that and not need to ask.
How about pointing us to some of your pics that you are pleased with and some that you think ought to be good but miss the mark for some reason - perhaps that you think may be due to an equipment limitation. Then some of the experts could perhaps offer a more specific recommendation?