Plum District is offering a free $10 credit to new account sign ups. You can hold on to this credit until you see a deal you would like to grab or you can consider these:
Free Kiwi Magazine subscription (on sale for $6, free after credit)
$32 voucher to Pedoodles Shoes website for $6. On sale for $16, only $6 after credit. Shipping for a pair of shoes runs about $4.