I use this one to carry around my 2nd body with a 300mm f4 L ( a bit longer than your main lens) attached, plus a few bits and pieces and a 17-40mm or longer lens can fit in either of the end pockets.
Its not a camera bag but is comfortable to carry and does the job.
You can't go wrong for £7.95!
Buy your Heavy Duty Canvas Haversack at discounted price from Surplus and Adventure online superstore