one of my 'hobbies' is accumulating small seat packs lol
I used the Cannondale seat pack at top right for years ; held multitool, tube, two levers, patch kit, two co2 cartridges, qwickfill, etc
had a small leather strap sewn on to the back part of the pack so I could attach a small taillight (at the time seat packs did not have these attachments)
the three packs bottom left (and top / second from right) are slim/narrow packs that have a 'vertical' profile when installed