Old rattle cans?

I found a box spray paint in my store room.

Must be 5 years old, some cans older than that.

Toss it?

Not until you give this a try. Fill kitchen sink with warm/hot water (a temp like you use to wash dishes). Let the cans warm up for about 4-5 minutes. Rattle cans vigorously for a minute and place back in water for another 5 minutes or so. Rattle cans again and test spray on some kind of scrap cardboard or whatever you have. Be sure the nozzle is clean also. Some nozzles are acetone resistant so you might want to soak them in that.

Be wary as well.

While they may all be good & full & willing to nicely spit paint, older formulas (Looking at you Krylon...) can have detrimental effects on newer paints, either under or over.. try to keep the same brands & eras together..

Some are lacquers, some are enamels, some are some other type, and not all lay on top of the other nicely..

I have rattle can paints some open some new that are 20years old. I've used them successfully on many projects with caution. First shake for about 5 minutes. Test spray on scrap material to see it the can has propellant. If it does, soak in hot tap water for 2 to 4 minutes to increase the internal pressure. Spray away then let the paint set overnight to ensure old solvents disapate.