For purchasing on tablets/phones Amazon also has a cool security system whereby after you make the purchase they text you a six number one time use code to enter in the Amazon app. So unless the their or finder of your lost tablet has your phone, they won't be able to complete the transaction. I cannot remember what Amazon calls this security option, but, I use a similar one for various other accounts too. I had some jerks hack into my GoDaddy FTP account and they were able to install malware on my part of the GoCrappy web server. After I discovered and deleted it I started using GoDaddy's Two-Step Verification of security I described where they text you a one time code to enter. Since starting that I've had no other hacks into my website.

ETA: They call it Two-Step Verification. Here is their website on using it.