The fall foliage show of reds, yellows, gold have begun to subside and soon enough a night of below freezing temperatures will bring that to a close and all those leaves will end up in the landscape.
If you are out there in the country with natural woodlands, leaves play a part in preserving the natural habitat of native trees, shrubs and flowers. If that is the case, just let those leaves lie. The leaves will decompose and return valuable nutrients to the soil to be used by the soil microbes that in turn support plant growth.
Where your lawn and trees exist together, mulching the leaves with a mower lets the small pieces fall between grass blades, benefiting the soil, trees and lawn. At some point there can be more leaves than can be mulched in. This is the time then to mow and bag them so the leaves do not smother the lawn.
Where the vegetable garden is adjacent to the lawn, consider either mowing or blowing the leaves in to the beds to be worked in either yet this fall or left as a mulch layer for the soil and worked into the soil next spring. Whole leaves can be used as mulch around the base of tender plants like roses. You use the whole leaf as mulch so it does not pack down, defeating the purpose of protecting the crown of the rose plant.
Now back to the leaves you have collected with the lawn mower. Consider using them to start a compost pile or build upon the one you already have. That bag contains the two primary ingredients, browns and greens. When considering where to place the compost pile or bins, think about the shady areas in the yard where the grass does not do well anyway as a possible location. The traditional compost pile will need to be four to five feet square at the base to be large enough to support composting with a height of about four feet. As you create the compost pile, some garden soil should be sprinkled in as you go to provide the pile with the microbes that will be breaking down the organic matter into compost.
Since organic matter is naturally acidic, about ½ pound of a finely ground limestone should also be added for every cubic yard of material. Your compost recipe is almost complete. Once the composting pile has been created, the final ingredient needed is water. If the pile remains too dry, no breakdown occurs. If left too wet, an anaerobic condition and decay occur, giving you a very smelly, slimy mess to deal with.
Fresh kitchen produce peelings can also be added into the compost pile year round. They provide some of the moisture that is needed during the summer and after they have frozen and thawed from the winter months, provide moisture as well. If you are lacking in the fallen leaves department, just ask the neighbors who have bags sitting out at the curb. Don't let that good organic matter get away, build a compost pile.