Cheap and Easy for Hot:
Rode out to LA from Colorado in early August back in '94, and it hit around 121-123 degrees F around the St. George, UT area. Survived by having large sports bottle filled with water, doused myself every 20 to 30 minutes.
2015, early July, picked up my wife in Orlando, FL, and we rode back to CO in mid-90 F temps. She came up with the marvelous idea to pour large McD's cups of ice (after we got done guzzling iced tea) in the inner mesh pockets of our mesh coats. Turns out ice works even in high humidity... You were cool for an hour or so and then you were just rather moist.
Cheap and Easy for Cold:
Stop at a 7/11 and buy the thickest newspaper they have, and stick it inside your coat against your chest. Works best on an un-faired bike, obviously, but it always helps. Light-weight backpack, packed lightly so it's still comfortable, helps alot as well.
Oh, yeah: Don't forget to open your heaters. The little rectangular plastic covers in the bodywork. The shop manual will tell you these exist for carburetor tickling, which they do, but at lower speeds, this works nicely--aka, better'n nothin'...
