As far as desserts, about the easiest thing you can do is a cookie cake.
1) Go get a bag of Nestle semi-sweet morsels and follow the recipe on the back. And by "follow the recipe", I mean this:
A) Put all ingredients except for chocolate chips (and nuts, if you like those) into a large mixing bowl. Mix well.
B) Add chocolate chips and mix again, just until they are evenly distributed.
C) Taste liberally.

2) Dump the dough into a pan - you can use a casserole dish, or shallow cookie pans, or whatever you have. Smoosh the dough around until it's more or less flat, and fills out all the corners.
3) Stick it in the oven (recipe temp is.. what, 350 degrees?) for about 20 minutes. Continue cooking in 5-minute increments until the top looks like the desired level of brown. (more brown = more crunchy, but it's pretty hard to actually burn them unedibly in pan form!)
4) Decorate:
A) Grab some baking chocolate chunks, drop a few of them in a ziploc sandwich baggie, and microwave until melted.
B) Snip off one corner of the baggie, and drizzle chocolate in broad stripes across entire cookie cake.
C) Repeat with white chocolate chunks (as desired), making stripes in the opposite direction.
D) Sprinkle with baby M&Ms or equivalent, for color.
It's easy to do, hard to screw up, and tastes amazing. If you like soft and squishy cookies, consider adding an extra tablespoon or two of butter - delicious!
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Or if you have more money than time/energy, Sam's Club tends to have excellent desserts.