One important thing to remember when flying is that airline baggage fees are charged both ways. So, if your outbound flight charges you $30 for your first standard checked bag, expect to pay another $30 for that same bag on your return flight back home (that's $60 bucks, roundtrip).

If your travel is booked on a single ticket (one reservation), you generally do not have to pay for baggage twice, even if your journey involves connecting flights or "codeshare" partners like British Airways or Iberia. Your bags are usually "checked through" to your final destination, and you pay the applicable fee at the start of your trip based on American's baggage policy. However, if you have booked your journey using separate tickets (two different reservations), American Airlines will typically only check your bag to the destination of the first ticket. In this case, you would be required to claim your bag at the connecting airport, exit the secure area, re-check the bag with the next airline, and pay their specific baggage fees, which could result in paying twice. This also applies if your connection is with a non-partner airline with whom American does not have an interline agreement. Always ensure your flights are on one record locator to take advantage of the "through-check" policy and avoid the logistical and financial burden of paying twice.