Hi all, I'm new to DSLR photography. Just got my Canon 60D with EF 24-105mm f/4 L IS USM recently.
Here's my humble 2c worth:
Before purchasing anything else, get a dry cabinet ASAP to protect your investment. The hundred odd dollars spent protect thousands.
Between bag or tripod, it depends on what genre of photography you are currently pursuing.
If you're into fireworks, timelapse & night photography, a tripod is an ABSOLUTE MUST.
For landscape, architecture, studio, product, food, macro or any photography which involves static subjects, a tripod is a good-to-have unless there's a good amount of light. In which case, you can get away with handheld.
Even with the high ISO capabilities of our DSLRs allowing us to capture decent images handheld, you may mind the graininess of the resultant images, which can be minimized with lower ISOs requiring a longer exposure. That would benefit from the stability of a tripod in order to prevent camera shake (even if your lens is equipped with image stabilization).
Action photography can also benefit from a monopod to help relief the weight burden of a long telephoto and allow smoother swiveling when panning for that background blur action shot.
Street, photojournalism are some genres which do not need a tripod.
Bags are just there to protect your gear during transport and travel. Unless you're a pro or a well-heeled enthusiast who travel with multiple bodies, primes and telephotos requiring a trolley bag, any bag is fine, be it a freebie that comes with your purchase or a pre-owned bag from CS Personal Classifieds.
Try to get the best tripod you can afford as a good one will last for years and served you well. You'll need to trust it to support thousands of dollars worth of gear atop it. A carbon fiber tripod would be great for superior strength, rigidity and lightweight. Moreover, with the abuse tripods can take, carbon fiber will take the inevitable nicks a bit better than anodized magnesium alloy or aluminium from a cosmetic point of view (or so I'd like to imagine).