Properly secured I'd also expect a typical can to take the g-loading. It's the securing I'd worry about.
A typical 20 litre can, when full, weighs about 17kg. At 9g that's 153kg - some fairly secure tie-downs are needed there ! Even a 5 litre plastic can at 9g is 36kg, 60kg at 15g - and that will smart a bit if it's tied down behind you and comes loose.
Conversely however, at standard crash loads a normal seat harness should be designed for an absolute minimum of 693kg forwards - so a 20 litre tank full of, say, water should properly strapped in be quite safe in a seat harness. But probably not in the baggage tie-downs.
G