40/2.8STM is basically my do-it-all FF prime kit lens (aka body cap pancake
), but sometimes my mood changes and I use my Sigma 150/2.8Macro for everything, specially outdoors (yes, I do mostly macro and people). So, I could live with these two. Stitching and cropping works well for me. Otherwise I would use Samyang 14/2.8UMC and 85/1.8USM. However, before buying any new lens, I would wait for Photokina. Some say Sigma will bring some new toys, like 24/1.4ART and maybe 85/1.4ART.
For 1 prime kit - a single 50/1.4 should do.
For 2 prime kit - your 35/2 IS USM and 100L Macro may work fine (I'm not a fan of this 35mm bokeh).
For 3 prime kit - I would add something wider 14, 20 or 24, your choice.