I bought this micro USB from Amazon. Flap closes down fine so it is hidden away and I just leave it plugged in.
SanDisk SDCZ43-016G-G46 Ultra Fit USB Flash Drive, USB 3.0, 16 GB https://www.amazon.co.uk/dp/B00LLEN5FQ/ref=cm_sw_r_cp_api_4GplxbAHFQZQ3
Loaded lots of MP3's and films to keep my little one amused and it loads instantly with no problems.