In general they are complete, but there are a few different kits and some are more complete than others
In any kit there will be things that you will WANT to upgrade over time. But for the most part any beginner's kit should have the basics needed to do the job. I'd suggest getting a kit to fit your brewing style. For instance:
I'd go with buckets only, to start with. I ferment in buckets and a glass carboy would not be used for making almost every beer I brewed. And buckets are cheaper than Better Bottles and just as useful IMO.
I'd make sure the kit had the tubing necessary to rack beer and an autosiphon to make racking cooled wort/beer easier. You gotta have a hydrometer too.
Make sure you get two buckets, a 6.5 gallon or larger for fermenting in, and a 5 gallon for bottling in. Also a bottling wand is mighty handy at bottling time.
And you need a capper of some sort. And a way to sanitize everything. I use StarSan and recommend it for cost and ease of use.
That's a pretty basic kit. Some might like to go with better bottles, or even glass carboys for various reasons, but that's a personal preference, not a major upgrade IMO.
Most all of the online places have comparable kits, but FYI Midwest has Groupon deals pop up all the time and they are great ways to save money on a starting kit.
Also know that no matter what you get you will probably want to add to it or upgrade certain things down the road. It's the nature of the hobby.