One of the most hotly debated topics of all experienced divers is how they configure their equipment (equipment configuration). However there are 3 issues all experienced divers will agree to when talking about solo diving configuration.
The additional mandatory equipment required for the solo diver is a surface marker buoy (SMB), a reel, and a surface audible signalling device.
One popular and functional way to carry a stage cylinder is to have it slung at one's side much the same way as technical diver's carry stage bottles for decompression gases.
In SDI's opinion - and this is something you may wish to discuss with your instructor and other experienced divers because all input is valid - the best solution for the single tank diver is the use of a separate small volume pony bottle (sometimes referred to as a stage or sling diving bottle).