Garlic. Garlic goes with everything. The best is fresh, ground with something rough (mortar & pestel (sp?), FI), but the jars are OK. Dried up isn't worth bothering with. If it's a simple dish, try putting in garlic in parts, so in the end, there's mush, well-cooked, and near raw garlic. Garlic is also one of the few foods we've got that is very good for you from raw right up until it's charred.
If you have somewhere near by like a whole foods, get fresh garlic and learn to peel it (it's just practice with a big knife, and once you get it, you'll not need anything but fresh, except for back up). Here, I find the garlic from whole foods or international grocers lasts months just fine, yet that is not so for any major grocery stores.
Kosher salt, sea salt, etc.: must have. You may not notice anything right off, but when you try to go back to not using it, you will. Pepper and a grinder ends up the same way--novelty right off, but once you're used to it, you can tell the difference.
Oregano, basil, thyme. Fresh is required for simple sauces (like pesto), and fresh foods, but dried is about as good for anything that cooks a lot.
Rosemary and parsley work very well for fast cooking, like grilling, browning, and searing.
If getting powdered stuff, go to some international store and get either stuff they make, or the somewhat large quantities. FI, the bags of Indian chili powder, with almost no English on it, is very good, but nothing in jars I've found is. I've done this for mustard seed, cumin seed, and ginger, too, same results. Nothing is as good as cutting it up yourself, but it can be close enough to not be worth the trouble most of the time.
More off-topic, if making dishes in a skillet often, go get a cast iron skillet, and learn its ways. My cast iron skillet and dutch oven are my go to pans for any fast meals, now, but they do require some learning (read: failures along the way). Nothing gives a good roux like iron.