So far we have:
It turns out that most airlines we travel are connected with one of these 3 miles programs.
Then there is:
Wyndham Hotels membership.
They give us points for extra stays at their hotels or convert the points to miles towards any of our current mileage programs.
Our mileage programs also have other ways to gather miles:
Dining programs, and shopping programs.
Shopping: You register on your mileage program website, and every time you want to shop online, go on their website first, and check whether the store you want is there. Then go to the store using their link and make the purchase that way. You make miles for every purchase done this way.
Dining: You register on your mileage program website, and register a credit card with them - it has to be a different credit card for each program. Every time you want to go out for dinner, you check their website first for a restaurant near you. If that restaurant meets your needs and is giving out miles on that day and time, then go for it and pay with the credit card you have registered.
Your miles won't expire as long as you keep adding miles to them. So this is what I do - I have a chart with our miles and the cards linked to them. When the miles are about to expire (because we haven't flown in a while) I go shopping or go eat out with my husband.
Just this Christmas we did our shopping through Dean's AAdvantage eShopping, because his miles expire in February. We found all the stores we usually shop at, and we bought stuff we definitely needed.