allowed components that may be freely added or removed are good ballast - cool suit coolers, fire systems, oil accumulators (accusump), mufflers, sway bar brackets, strut tower bars... just keep it tolerable and most of the time you will be found compliant. exploit hard and you can get dinged. actual ballast, as in material added specifically to meet minimum race weight must meet ballast rules in the ITCS, 9.1.3.D.9.l - 50lb sections max, removable, 2, 1/2 in grade 5 bolts, big washers, lock nuts, etc... usually this will be gym weights in some sort of containment system, plates of metal, lead bricks, shot-filled boxes, etc... google ballast box for some good ideas but remember the IT rules when you implement them, they are specific and unique.

unfortunately, AJ's ballast stack was illegal as ballast must be retained by 2 or more 1/2in grade 5 or higher bolts in IT (9.1.3.D.9.l.2)

I run a 3Qt accusump in the "frunk" of my MR2, slight weight shift. big oil cooler, steel radiator over Al (not overheating, weighs more), cool suit cooler in the frunk, etc... move legal weight forward. I have a ~33# lead brick bolted just forward of the forward seat mount cross brace up against the rocker.