I would say it all depends on what you plan on shooting. If you plan on taking pictures of landscapes and outdoor stuff, I would buy a tripod. If you purchased your camera to take pictures of your kids or something like that, I would get the flash first. Getting an external drive would be a very close second. I had a failure of my hard drive shortly after I started taking taking photos of my first born and didn't have a backup solution. Luckily I had a ton of memory cards and wasn't deleting stuff of them but rather just switching them out until they became full. I luckily didn't loose anything of value in the failure but learned the lesson about having backups.