My first century was in the mountains solo with 9400 ft climbing, and no cell reception.

Brought a small messenger bag with extra tire, tubes, hex keys, zip ties, spoke wrench, chaintool, flip flops, few extra waters, a few bananas, pb sandwich, a few gels, extra jersey for the ride down, and a knife. Probably 12 lb extra.

I ate all the food.

Other solo centuries such as to Santa Barbara and back, just brought tube, tools, water, banana, and some gels.

As others have said, if you can do 85, then you've basically done one already.