Over time I've found myself making more ambitious recipes, and these days I often don't follow recipes at all, I like knowing the ratios of ingredients and flavors and creating tasty things from scratch. I cook for myself most of the time, which makes this approach work...if I mess up on a new improvised recipe, I just have a less-than-perfect dinner. Then, when I'm cooking for friends, I'll whip out a home grown recipe that I've made enough times to trust.
I've found paper cookbooks preferable to apps, because I can spill stuff on them, burn them, use them with wet hands, set stuff down on them, and they don't turn off. I have a couple of cookbooks with simple, staple recipes that I use for reference, but I've also found The Flavor Bible(1) to be incredibly useful—it basically works as a big index of ingredient affinities, so you can look up flavors that go well together for a huge variety of ingredients.
I keep my kitchen stocked with a lot of basics, but I live right near a grocery store, so I'll drop by after work if I need anything special.
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