Retaining rod straps can be bought separately but they also come with some chimney rod sets. The more rods you have, the longer the retaining straps will have to be.
Wonkee Donkee has found an alternative use for a retaining strap!!
Chimney rod bags
A good chimney rod bag is essential to help prevent loss of rods, and ensures you always have all the rods and tools available when needed. Chimney rod bags can be bought separately but they also come as part of a set when you purchase a complete set of rods. There is not normally anything printed on a bag to indicate its size or how many rods it can hold, although the average bag can accommodate up to 10 chimney rods and approx 4 drain tools, depending on their size.