Here is a portable HardDrive I was thinking of buying. My guess is that it has been formatted to NTFS. IIRC you can't read or write (or is it just write) to NTFS with a mac without a 3rd party SW like Paragon NTFS for Mac.
Anyway- link here:
https://slickdeals.net/deals/external-drive/
Some tips if you want to go this way ($20 + Shipping for 1TB is a mind blowing deal).
1) Read the First Post (OP)
2) MAKE SURE YOUR READ THE WIKI (right below the OP) A FEW TIMES. This deal involves rebates and a subscription which CAN be cancelled (if you have a prepaid debit card (like a VISA GC or something) than you can use that as long as it has a $1 on it or something)... But if you read the wiki and follow the steps you can make sure that you won't get charged (by cancelling subscription).
3) Don't forget to go through a cashback site. Discover = 5% cashback.
4) You will be submitting two rebates (= each rebate goes in separate envelope)
If you do go this way, I highly suggest you create an account and post if you have questions over there, but I'll be here to also help out
My suggestion would be to make this a 'throwaway' HD since it's cheap... invest in something a little more expensive (like a well known External Desktop Hard Drive (not portable) and get this too... Since this is portable, you can take it with you everywhere.