a woman holding a computer on her legs with Voyage PriveĢ website

When booking a flight, many of us choose to fly with the cheapest airline flying on our chosen dates — but to ensure you don't encounter tons of additional costs on top of your ticket, it's important that you do your research beforehand. For example, which airlines have free checked bags and which do not, and which airlines allow you to choose your seats beforehand, and which are first-come, first-served. To ensure you're not totally blinded by the cheap flight tag when booking a flight for your next vacation, we've outlined a few must-knows below.

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- Seats are not assigned (so it's first-come, first-served)
- No checked bag fee for your first two suitcases
- A third suitcase will cost you $75

Cape Air
- Free checked bag on domestic flights
- Second and third bag cost $40 respectively

- Extra-space seats start at $10 each way
- The cost of your first checked bag varies but is usually $25
- Your second checked bag is $35 each way
- Three or more bags will cost you $100

Virgin America
- Preferred seats are $10-$40 based on flight
- First, second and third bag cost $25 respectively
- Depending on your ticket, you may also be entitled to one free checked bag

- You will need to purchase a seat (price varies)
- Only one checked item accepted per person
- Additional checked bags can be purchased on a first-come, first-served basis