Unless you're a master at minimising your commuting clobber, you'll probably want a backpack or panniers for your ride to work. Each approach has pros and cons.
Whichever you prefer, check the capacity you need. Collect your commuting gear and eyeball the pile. If you want to be precise, put it in a cardboard box and measure its length, width and the depth it's filled to, then multiply them. Use centimetres. That will give your load's volume in cubic centimetres. Divide that by a thousand to get the volume in litres.
All commuter bags benefit from being rainproof. If the bag you fancy is not itself waterproof, check that it comes with a rain cover. Reflectivity is useful, particularly for backpacks as they can obscure conspicuous jackets.
Carrying the load on the bike instead of your back is easier on your body, because you've got less weight bearing down on your shoulders, backside and hands. You'll sweat less too. The further you're riding and the more you're carrying, the stronger the argument for panniers.
Two small panniers are more practical than one big one. Your bike will be better balanced and you can divide the load: work stuff in one bag, bike stuff in the other. Small panniers also provide more heel clearance. That's important if you've fitted a pannier rack to a bike with relatively short chainstays – such as a road bike or cyclocross bike.
If the bag will double as your briefcase, get an office pannier: a rectangular, sober-coloured bag with internal dividers and (usually) a padded laptop pocket. Otherwise, ordinary panniers are fine. Look for durable, waterproof material, and attachment hooks that go on and off the rack easily when you want to (when parked) and never when you don't (going over a bump). Pockets are useful to prevent having to dig around for small items like a phone, wallet or tools.
Backpacks are convenient for short trips, particularly those where you're on and off the bike, because the load goes with you as you stop. They enable you to commute on a bike won't take, or simply doesn't have, a pannier rack – for example, many road bikes, mountain bikes, and folding bikes.
Backpacks are more comfortable than courier bags as both shoulders bear the load. Courier bags give quicker access to contents, as they can be swung around your body and opened while being worn. But for A to B trips, a backpack is better.
Backpack shoulder straps should be broad and comfortable. Look for a waist strap and/or chest strap too. These will hold the bag snug against your body, enabling you pedal rapidly and to ride on the drops without the bag bouncing around. Some padding is useful to stop things poking in your back, but take any 'ventilation channel' claims with a pinch of salt: if it's hot or if you're riding any distance, you will sweat. It's no coincidence that many backpack-using commuters cycle in bike kit rather than normal clothes.
Here are some good examples of panniers and backpacks for commuting.
Ortlieb Front Roller City
Like all Ortlieb gear, these small panniers are completely waterproof. They're made from tough, PVC-coated polyester and PU-coated nylon, with the seams welded together. The top rolls over and buckles down to so rain can't get in here. Lifting the handle retracts the rack hooks, so each bag can be removed one-handed. There are Scotchlite patches outside but no pockets inside. Capacity: 25 litres per pair.
Cyclescheme Price: £44.25
Altura Dryline 32
They don't have the shiny PVC feel of the Ortliebs, but these Altura Drylines are as waterproof as the name states. The main compartment has a drawstring-and-lid closure, so you can overfill it a bit if you want, and there's a useful outer pocket. Though sombre, they have reflective trim for nighttime visibility. The base is well reinforced to prevent wear. Rixen Kaul Klick-fix hooks are an industry standard. Capacity: 32 litres per pair.
Cyclescheme Price: £61.27
Carradice Super C Universal/Front panniers
A favourite of touring cyclists for their toughness and longevity, Carradice's Super C bags are equally suitable for commuting. They're made from cotton duck – a durable, waxed-cotton fabric that shrugs off rain like its namesake. There's an outer pocket for tools or other small items and 3M reflectives front and rear. The simple, secure hooks will fit racks up to 13mm in diameter. Capacity: 28 litres per pair
Cyclescheme Price: £67.50
DHB Waterproof Rucksack
Like the Ortlieb pannier, this rucksack uses waterproof fabrics, welded seams and a roll-top closure for complete imperviousness to rain. A moulded foam back makes it comfortable, while a waist strap keeps it stable. There's a thin outer pocket with a waterproof zip but no inner pockets. It also has reflective patches and a mount for a small LED rear light. Capacity: 25 litres.
Cyclescheme Price: £61.27
Brooks Dalston Knapsack Small
Named after the hipster haunt of Dalston in London, this premium-priced backpack offers substance as well as style. It's made from waterproof fabric and leather, and there's a chest strap to stop it moving on your back. Although small (12 litres) it has a 13in laptop sleeve and three wide pockets inside and two pockets big enough for a bike bottle outside. Similar, bigger bags are also available form Brooks.
Cyclescheme Price: £81.71
Henty Wingman Backpack
This is a tarpaulin suit-bag that goes on your back. It will accommodate a suit and one shirt or blouse or three shirts/blouses. You put them in flat, then roll up the bag into a tube, keeping creases to a minimum. A removable 12-litre utility bag for other items goes in the middle. Features include chest and waist straps, a 13-15in laptop pouch, a removable phone pouch, a hi-viz rain cover, and a folding coat-hanger.
Cyclescheme Price: £91.91
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