Racks and Panniers
Panniers are storage bags for your e-bike. Rear racks and pannier bags are by far the best way to transport things on your e-bike. While backpacks can work the extra weight they put on the rider can be uncomfortable and makes it slightly more difficult to ride.
Rear racks come in 2 basic styles. One that mounts off the seat post alone and is generally good for up to 20lbs max and the style that bolts to the frame below the seat and just above the rear dropouts that can handle much more weight.
Mounting your rack
Mounting a rack to your bike is a very simple process that requires very few hand tools outside of an Allen key set and maybe a wrench. Racks mount to 2 threaded holes in the frame just behind and below the seat, as well as two threaded holes just above the rear axle.
If you lack the hole on the upper part of your frame near the seat often your seat post clamp can be replaced with one that has the required mounting holes. Do note that you will have to measure your frame as seat post clamps come in different sizes.
If you lack the lower mounting points, P clamps or a rear rack with clamp on support tubes can be used. Please note that if you have rear suspension that you are pretty much limited to the kind of rack that clamps on to the seat post and has no side supports. Seatpost only racks generally bad to mount side panniers on as nothing stops the pannier from hitting the rear tire.
What rack is right for you?
Your rack has to physically fit your bike. This means your bike must have matching mounts and at the right width apart. The rack must also clear the rear tire. Most racks are designed to be adjustable from 26" to 29" tires, but some may not. Do check the description before buying. It is also important to get the width of the rack correct. Fat bikes will require fat racks, and some bikes put the rear disk brake in a place that obstructs some racks.
Here are some examples of rear racks:
Rear rack designed for bikes that don't have any of the mounting points to install a rear rack: Amazon.ca Amazon.com (Different product on .ca vs .com but visually seems to be same product). Note that you can not adjust the angle of the rack to the seat post on this style of rack.
What pannier bag to pick?
Consider your shopping requirements when buying panniers. Make sure it is big enough for everything you plan to buy, some items like frozen pizzas won't fit in smaller panniers. Also consider you can wear a backpack as well for even bigger grocery trips for storing very fragile items like bread, or bulky items like 4L jugs of milk in the backpack while the rest goes in the panniers.
Here are some examples of pannier bags:
Note there are many other seat post clamps, racks and pannier bags available online. If you don't live in Canada/USA, consider ebay and other online cycling specific stores and your local bike shop. The local bike shop can be great as you can often test fit the rear rack by holding it up to your bike and make sure it will mount properly before buying it.