Thought I would give details on the items you will need to create through Combining. As the achievement states, you will not need to combine any items which don't require any of the Chem Fluids to do so. For example, although you can make Strong Chem Fluid by combining Separating Agent and Flame Rounds, it's not needed. The following is what you will need to combine and what it creates.
Herb-First Aid Med
Solid Fuel-Burner Fuel
Strong Chem Fluid:
Herb-Strong First Aid Med
Solid Fuel-Flame Rounds
Gunpowder-Enhanced Handgun Ammo
All the items are found through normal progression of the game. That said, you may want to keep track of what you have already combined, as creating an item then reloading your save to use the same ingredients to create something else does NOT count. Thank you to "Calex dEUS" for testing and confirming this (Refer to 1st comment).