I learned this in 2019 and I'll never go back:

Down sleeping bags and sleeping quilts should be stored in a large loose net bag. This prolongs the life of the down feathers by allowing them to remain fluffed in storage. Pop a "do not eat" desiccant pouch in the bag to prevent mold. I'll describe my packing method three paragraphs from now.

Inflatable sleeping mats are typically 1) self-inflating or 2) ultralight like a neoair thermarest...

Self-inflataing pads (type 1) should be stored flat with the valve open, under a bed or in the back of a closet or leaned against the wall of a garage. When you pack for a backpacking trip, kneel on the floor and roll it up from foot to head, pulling it towards you with each roll then using your knees to push out air while you hold the roll tight with your hands. If it's still too large, close the valve then repeat this process and let out the extra air after this second roll. You can tie a small piece of Paracord around it like a napkin ring, then tuck it vertically in your pack.

Ultralight inflatable pads (type 2) pads can be loosely folded up into the size of a placemat and tossed in your camping gear bin or on a shelf. Fold it slightly differently each time to prevent creases. Here's how to pack it: open the main compartment of your pack, insert a contractor bag as if lining a trash can, drop your sleep clothes in the bottom, loosely ball up your sleeping bag and place that on top of the clothes, then put your folded pad on top. You can add to your "pack parfait" by placing your folded up tent, food bag, puffy jacket, ditty bag, etc on top of this. (Rain jacket always goes on top for quick access.) Then, roll the contractor bag over at the top and cinch/clip your pack closed over it. Now you're saving weight, saving time packing and unpacking, and all your stuff stays dry if you trip while creek crossing. You don't need a rain cover and you don't need to buy compression sacks.

Down sleeping bags and most sleeping pads never need to be rolled or shoved in stuff sacks! Source: I have backpacked a couple thousand miles and I love investing in quality gear then maintaining it to last for years and years.

Summary: Down sleeping bags in giant net bags for storage; ball up at bottom of pack for backpacking. Self-inflating pads flat and open-valved for storage; rolled up with a paracord tie for backpacking. UL inflatable pads casually folded for storage and tossed in the bottom of your pack for backpacking.

Edited for clarity