A step up from improvised meals, in my opinion, are those baked goods where you just toss in a pinch of this, a handful of that, and wind up with dessert. For someone raised in the tradition of measuring cups, that's a pretty terrifying prospect [and mystifying process]. I do have two sweets in my arsenal that are more formula than recipe - the Tightwad Gazette universal muffins, which still makes liberal use of aforementioned measuring cups, and this crisp, passed on to me by a Swedish girl I met while WWOOFing in Washington State two summers ago.
1) Melt 1 stick butter [or you can use softened butter, I never plan ahead sufficiently for this]. Mix in flour and sweetener in a 1:1 ratio until the mixture becomes clumpy.*
2) Sprinkle chopped fruit or berries** into a 9*13*** pan. The fruit should cover the bottom of the pan liberally.
3) Crumble crisp on top of fruit. Bake at 350 until the fruit bubbles. If topping has not browned by this point, then turn oven to broil for a few minutes.
Fast, easy, versatile! You can use any fruit you'd usually find in a pie [although I've never tried citrus], any type of flour you have on hand [I love adding oats with a bit of wheat flour], and any type of sweetener too [honey, which I've never personally tried, will probably need more flour to compensate for stickiness]. Also tastes lovely with a scoop of ice cream or plain yogurt. Works well as a last-minute dessert, to use up odd leftovers in the fridge, to disguise mushy fruit, and if you're low on funds like most graduate students are, apples are an economical and filling way to stretch out berries and the like in the filling.
*If you prefer your desserts less sweet, like I do, then add less sugar:flour. If you like your desserts more buttery, then you'll want to stop adding sweetener/flour sooner, when there are larger clumps. Less buttery, look for finer grain clumps. The best part is that you can taste as you go to see if your topping is too sweet or not sweet enough, and adjust accordingly.
** If you have a wet fruit like berries, coat with a spoonful or two of flour so that it will become gooey upon heating. If your fruit are not terribly ripe, also coat with a spoonful or two of sugar.
*** Can also be made in an 8*8 pan. Just use less butter ... like 3/4 of a cup or so.
Note: in this photo, I didn't have much fruit on hand. Usually there'd be twice as much fruit in this kind of crisp.