You will need a junk e-mail address for using Cash Crate, unless you want your regular address constantly spammed. Since many Cash Crate offers come from the same site, you may be not be credited if you use the same e-mail address on multiple offers. I recommend G-mail because they have one feature other sites do not.
With Gmail, you can set up an e-mail address consisting of up to 30 characters. Gmail's special feature is that after you set up your e-mail account, you can edit the address by adding periods. This changes your e-mail address on the sites you input it into, but all mail is delivered to the same address.
For example, you can sign up with an e-mail address of firstname.lastname@example.org. When you enter it into a webside, simply alter the address by adding periods. You can use:
...and so on, adding as many periods as you'd like!