Replying to spray on water proofing

I just got a backpack for my back country outings, but it is not water proof. I have a can of scotch guard water proofing, will this work good enough to keep my stuff dry inside? any one have any experience wiht this stuff? I used it before and was not all that impressed, any other options?
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I smoke chewy like a mothafuckin nut
You got a gram bag hit the zags and roll her up
Cuz a nigga like me can't fake it when I'm high
Get the Visine for the tight red eyes
Jump in the Cutlass with the niggas from the set
The blunt went out but we ain't done yet
Get another one blaze like a barbeque beef
It ain't nothin like a blunt for the funk in ya teeth
Yeah, I'm a skinny 6'5 motherfucker
If you didn't know me you would think I was a clucker
But I'm not a clucker I'm a dodger and a ducker
Come a little closer I'm a show you I'm a punch ya
And if I can't beat you I get my gun and I'm a buck you
Turn you over like a little bitch and I'm a fuck ya
-Andre Nickatina