If you are considering applying in more than one field, you have a tough road ahead of you, and you should strategize accordingly. Remember that, although your ERAS activities cannot be individualized to different residency programs, your personal statement and letters of recommendation can. Demonstrating commitment to each field through your essay and letters will be a challenge, so take time to write thoughtfully, and make sure you speak candidly to your faculty recommenders.
Above all: Ensure that you assign the correct specialty-specific documents to the correct programs!