depends how much you bring, and your budget.
here's a tip, mil surp is shit tier for the money. Yes its maybe slightly cheaper? but an Alice + upgraded straps to make it comfortable = more $ than you're average backpack.
if your looking for a weekender, go for something in the 30-40 liter range, like an Osprey Stratos (couldn't be happier, $139 not on sale)
if you're going bigger, but still on a budget, try something in the 50 liter range.
Also, for your budget, check out
geartrade.com to find used backpacks and gear.
