If you plan to install a rear basket, it is necessary to purchase a rear carrier first to hold the basket in place. Once you have the carrier installed, use regular baskets, wire baskets, milk crates or even small plastic garbage containers as your carryall, according to bukisa.com. (See Reference 1)
Ensure the baskets you use are not too wide so you can zip between cars and other tight places with no problem. Width is important when mounting and dismounting a bicycle as well.
Attaching baskets or milk crates with zip ties is a great idea as there is no drilling or hammering necessary. Zip ties are very strong and weather resistant. Thread the ties through the holes in the basket or milk crate to your carrier. Ensure you have enough ties to tie the basket tight where there is no movement at all. This helps to provide balance and lessens the stress on the tires.
Use bungee cords to keep your stuff from falling out. Stretch one or two bungee cords from your rear carrier up and over your basket and secure. For weatherproofing, use a plastic sheet or plastic tablecloth to cover your basket before attaching the bungee cords.
If you want a bit more weatherproofing, look around your house for plastic garbage bags or an old plastic tablecloth to weatherproof your basket, according to etsylabs. (See Reference 2) Fuse several garbage bags or plastic bags you get from grocery shopping together using an iron on low heat and wax paper, and make the piece large enough to cover your basket. Fold in the edges of the bags, and fuse again. The rule of thumb is using six to eight bags to fuse and sandwiching wax paper in between the bags to strengthen the cover. Secure with strong string such as shoelaces by cutting small slits through the bags to thread the string, and tie one side of the cover to one side of your basket. Pull the cover over your basket, and secure it with string or shoelaces to the carrier.