Every year, in January, I replace life limited items, often taking that opportunity to adjust the kit contents based on new knowledge, new products or changing personal priorities. These are certainly not the ultimate kits, but are much better than what you would get in typical commercially assembled kits. What follows should give you a basic concept of the sort of items that could be included in a survival kit and how to select them.
Any survival kit is a compromise involving size, weight and cost.
With the information here you should be able to make an informed decision regarding what's right for you, given all these constraints. Many commercially available kits have deficiencies, either in what is included or in the quality or quantity of the equipment and supplies. In most cases, any standard kit you might purchase could stand to be supplemented in some manner or other, at least in part because everyone's needs are a little different. Some of the best smaller commercial kits do not include any water, for example, a vital survival resource you will need to provide yourself. Thus, you may be forced to locate such items locally to add to your kit.