It doesn't matter if you're bicycling for a marathon, or just pedaling down to the store, a bike rider needs a few things. Sure, you can stuff your pockets with items you need, like your house keys, money clip, change, and more. But, as any bicyclist knows, things in your pockets, at least while pedaling, can be a bit uncomfortable. What you need is a saddle bag. Okay, now that you're back from checking on the price of that, and as you're recuperating, go look in your kitchen. If you've got a jar with a lid you've got a cheap, unconventional, but useful saddle bag for your bike.
Face it, there aren't that many places on a bike where you can put a carryall. You can't hang it on the handlebars and deal with it swinging all over the place. And it's a tall order to attach a container with screws, to the frame. But you can make a helpful saddle bag – even though it's a non-traditional type – from an empty potato chip can, an oatmeal tin, a plastic jar with a lid, or a similar container. Use the common container as your saddle bag and you'll be able to store all sorts of things while you ride.
If you keep your bike in a place that is out of the weather you can consider a jar or canister that could be ruined if it got wet, like a potato chip or oatmeal canister. But if you ride in the rain, or leave your bike outside in the elements, use a plastic jar with a lid. You could even use a plastic bowl with a tightly-snapping lid. No matter what type of container you use, attach zip-ties to it and you'll be able to connect it to the bicycle. If you're using a plastic bowl and lid, cut two short slits in the top of the lid. If you're using a plastic jar or canister-type container, lay it on its side, then cut two slits in one side across the width. Leave a few inches between the two slits but make the slits the same length.
Under the seat of a bicycle is where you can find a place to zip-tie the container to the bike. Thread the zip tie through the slits, hold the container under the seat, and zip-tie it to a hardware piece under the seat. Now you can ride a long ways, or just down the road, knowing you have everything you need, right under the bicycle seat.