I have the Bontrager BackRack S, which weighs only slightly more than the BackRack Lightweight and costs less. The BackRack S felt lighter than the Topeak and other brand my LBS carried. My bike weighs close to 30 lbs, so I doubt I'd notice the difference. But I figured I might eventually move it to a lighter bike and convert my current bike to a full time utility hauler with a heavier rack.

But it's been a good rack, very sturdy and easy to set for my bike's compact frame. I've carried up to 40 lbs on it, between 20 lb jugs of cat litter, sacks of potatoes and other groceries. No problems. I keep a cargo net over the top so it's handy for quick errands to pick up just one bag of stuff.

If you start shopping errands with your bike you'll probably start thinking about panniers, but may not want them on full time. I used a large homebrewed trunk bag for awhile but got tired of the hassle of securing it, which could take up to 10 minutes to rig properly.

So for quick trips recently I've been using a pair of Nashbar Townie panniers. Easy on, easy off in less than a minute, and very secure, or easy to carry into the store to fill directly. These are open top, collapsible panniers intended mainly for shopping, not touring -- although they could do in a pinch in fair weather (the cordura/ripstop nylon and plastic stiffeners would hold water if it rained!). They're designed for a traditional paper sack, and are about half the height of a typical Braum's or similar paper sack (Braum's is less than a mile away and I prefer their bread and prices on ordinary fresh veggies like tomatos). Or they'll hold around four plastic bags full. I use a cargo net to hold other stuff on top of the rack, when I'm not also using a trunk bag. Great for short errands and to get the blood circulating.

A couple other manufacturers make similar shopping panniers, sold on Amazon. At least one was designed like a tote bag, including shoulder strap.

They looked pretty good but I'm satisfied with the Nashbar bags. I've ridden a few times with the empty Townie bags collapsed flat, including in stiff winds, and hardly noticed the weight although they did catch a few strong sideways gusts. Even folded flat they'll carry my rain jacket/windbreaker, spare tube and patch kit without getting bulky.