Although there are subtle things here and there that make a backpack more suitable for bikes, you can definitely go without one.
I think the most important thing are chest straps with buckles. They keep the shoulder straps from sliding off. Waist straps/buckles are also good to keep the weight off your shoulders. Just tie down any extra bits that are flapping around.
I use my regular backpack to commute to work. It's not an issue at all, i just tighten the belts so that it sticks to my back and does not catch in the wind. The belts fly a bit behind but the only reason I know it is because i see it in my mirrors; i don't feel it. If it can help it's a Targus but really it has nothing special except maybe being a bit flat, not big at all:
why would you wanna carry your helmet around anyway just latch it onto your bike and forget about it. only thing that goes with me is my jacket because there is no way to secure it to the bike. but as far as your question goes i have a bugout brand back pack it has a spot for a removable bladder if you wanted to fill it up with water for a long trip or watever, it has several pockets and has shoulder straps chest strap and waist strap when you snap everything and snug it down its not going anywhere i think i paid around 70 bucks for it
I don't like leaving my helmet attached to the bike; too easy for mischief to occur. I usually just carry the helmet like a bucket containing my gloves, sunglasses, and keys, and wear the backpack (I admit it, my man-purse!) into whatever establishment I'm patronizing.
would you rather mischief to occur on a 100-300 helmet or a 4000-18000k bike which you have to ride back and forth from whatever establishment your patronizing in. i would much rather them mess with my helmet steal my gloves etc vs messing with my bike thats just my .02 cents
I would suggest a water proof or at least water resistant back pack. Also, a bright color will help people driving cars notice you. I have a small to medium size bright orange North Face hiking backpack which is awesome.
I personally use my Hawg NV from camelbak. It's a great bag with a ton of usable space, designed for mountain biking, which I also do. But it's great at any event really, and keeps my back sweat free due to the back design... expensive yes, but so far worth every penny
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