Duffel bags are easy to squeeze into tight spaces. The material of choice for this bag is canvas and it holds 45 litres.
From Amazon
Quadra Vintage Canvas Holdall Duffle Bag - 45 Litres (One Size) (Vintage Brown)
OnBuy
(One Size, Vintage Brown) Quadra Vintage Canvas Holdall Duffle Bag - 45 Litres