What to take for an ear infection for a plane trip?

Decongestants: The key is for the eustachian tube to be open. This is the tube that connects the inner ear to the nose and allows the pressure to equalize. This is what you do when you "pop your ears" with altitude changes. You can use a decongestant/spray to help clear them and chewing gum and yawning can help the process.

Nothing: If you have an ear infection there will be a mucus accumulation in the middle ear space. That mucus will buffer any pressure effect you may be accustomed to with flying. The fluid is not compressible like air & it does not leave the middle ear during flight. Ibuprofen or other med for discomfort is fine, but the ears shouldn't require special attention.