The first thing I learned when I started to travel for business was the value of joing every traveler program I could.
Many of the programs have such high minimum stays/miles/days that the average vacation traveler never hits any rewards, but one short trip can earn you more than you think.
First, Airline Miles: this seems obvious but you would be amazed how many people I travel with that aren't members of any program. Due to our limited flight options from Wyoming I mostly fly United. Many of their services are average (at best) but as soon as you meet their first "Elite" goals (35,000 miles) then you automatically get seated in Economy Plus, with no extra costs. This is a luxurious 5 extra inches of legroom. For a 6500 mile Hong Kong flight it may be the difference in sanity and craziness. Hint: Always ask which "Alliance" an airline belongs to. Don't make the mistake of getting a United and a Lufthansa FF Card since they share you can use 1 for both, but cannot combine later (I will do a more detailed entry on this later)
Second, Hotel Rewards: I made the early mistake of choosing Miles instead of Reward Points when I stayed at Mariott. Because I stay there so often I lost a lot of free nights, and ended up with a few thousand measly miles out of it. I still have a few programs that I have set to miles because I stay there infrequently. But if I plan to stay more than 3 nights a year at any chain I choose rewards so I can earn free nights
Last, Rental Car: This is by far the easiest. Sign up online to become a "preferred" member and you will get special service from your first rental. This usually includes express check-in (which has saved me many hours), free upgrades, and sometimes special covered loading areas. The rewards themselves are a little slow to rack up, but you can usually earn miles and rewards. I am a member of the Thrifty blue chip and I get a mile per $ spent and 1 free rental every 11 rental days. Since most my travel is to Asia I don't rent much, but when I do I am rewarded for it.
*Remember, your company cannot take your miles, or any other rewards you earn. These are yours to keep and use for PERSONAL travel.
After only 3 trips this year I have enough rewards to take all 4 of us on a domestic trip (includes 4 flights), 2 nights of hotels, and 1 car rental.
Lastly, I have 1 airline that I only aquired 3,600 miles on this year. Doesn't seem like that's worth anything, but I can redeem as few as 900 miles for subscriptions to some of my favorite magazines, that makes it worth about $20 per subscription, not bad.