I added the extremely fast (near SSD speeds) 256gb Corsair Flash Voyager GTX USB 3.0 256GB (CMFVYGTX3-256GB). Linus did a recent review of this extremely fast USB drive here:
Performance:
Transfer 2.44gb of 955kb photos: 38s read/115.5s write
Transfer 1gb video file: near instant read/12.4s write
Transfer 5.8gb video file: 13s read/67.2s write
Performance: Transfer 2.44gb of 955kb photos: 38s read/115.5s write Transfer 1gb video file: near instant read/12.4s write Transfer 5.8gb video file: 13s read/67.2s write