Well, most US airlines have miles that expire, but only if you have no activity in your account at all for some period of time (often 18 months). Any activity at all - not just flights - extends the life of all your miles. The notable exception is Southwest, which has a harsh expiration policy.
Luggage fees are tougher to figure, because in the current economy, they have been changing so quickly. Do you need to check 2 bags for free, or is 1 free checked bag enough?