Non-hypergolic liquid fuels i.e.:
LH2, LOX, Methane etc are all kept as pure as possible.
One of the major advantages of these is that they burn clean.
Any additions are potentially problematic: Complex combustion by-products, different density ratios leading to separation, and differential storage requirements etc seem to have outweighed any potential advantages to additives in modern rocket designs.
The slight exception is RP-1/kerosene.
This is such a complex mixture that its hard to tell what should be considered an additive and what's just part of the mix. The specifications for it don't say how you make it, just what it should contain. I don't know the refining techniques, and getting the desired ratios may well entail adding in the fractions you don't have enough of. However the list of chemicals its allowed to contain (https://nvlpubs.nist.gov/nistpubs/Legacy/IR/nistir6646.pdf if you fancy the long read) are all petroleum derivatives in line with what any kerosene would be expected to contain.
The party line seems to be minimising the 'extras' not adding them.
Hypergolics and solids are a different story. They already burn dirty and have additional problems that additives can help overcome. Consequently, both hypergolics and solid fuels very much do have additives.
In hypergolics there's a long list of things that are specifically added to combat some of the disadvantages of the base mixture. Most noticeably freezing temperature.
Solid fuel rockets are even more complex mixtures. It's common to add binders, catalysts and a host of other things to obtain desired physical, combustion, and handling properties.