I just use disposable lens cleaners that come in a foil pack. I have also used those lens pencils that have a brush and a cleaning solution in them but I find that they dry up every year and need to be replaced
I also use the lens cleaner in the foil packs for glasses.
The fogging issue is tougher - we would leave our guns in the truck so they were the same temp as the outside and try to not breath on it. Otherwise, no issues with fogging but did used to get snow in them hunting "the north woods" and would have to check and clear the scope or use a lense cover.