It's OK to say forget about them unless they are specially prescribed, but unless you've already had a DVT, or are in an high-risk category, you're not going to be able to get them on prescription anyway just for going on holiday. Personally, I think the best thing is to do the leg exercises whilst sitting on the plane, and get up and walk about as often as possible. I take an aspirin the day before and on the day of the flight.
It's important to see your doctor if you think you may be at risk of DVT, find out if the doctor can give you anything before you go.