Now that you have a blank canvas to work with, how do you jazz it up? Really, the only limit is your imagination. I used a baggy, faded boyfriend jean for a starter here. Since those have (as the name implies) a more masculine cut, fem it up with heels, a ruffle top and girly jewelry. (As much as the idea may repel you, rolling the cuff of boyfriend jeans so that your ankle is exposed will make them more sexy and less "I forgot to sort the laundry.")
The cut of your jeans does a lot to dictate the style of your outfit. Because of that, I rely on trouser-cut jeans to be my wardrobe workhorse. For the third ensemble, a chicer pant elevates the whole look. The details of belt, necklace and pumps make this a perfect look for running weekend errands without looking like you stopped in the middle of chores.
What can you do with a sweatshirt? Like tee-shirts, there's nothing wrong with a sweatshirt, but a plain grey marl will look ten thousand times better and less I'm scrubbing the bathroom today than a team sweatshirt. Personally, I think you shouldn't wear the same thing for cleaning that you wear for running to the grocery store. If you want to stick with sneakers, try colorful canvas instead of a running shoe. Sneakers and sweatshirts are both uber casual, but a long cotton skirt would keep with the relaxed vibe while still looking more playful.
Of course, when we're talking sweatshirts, I like to move out of Fruit of the Loom territory into something more structured. Starting with a good shape makes styling easier. As before, consider the cut of your pants. Since a sweatshirt is loose and long, pairing it with skinny jeans add definition. Think beyond the gym for your accessories. Add heels or gobs of jewelry, maybe flowers in your hair.
Everyone has a pair of cargo shorts laying around (and you probably got them on sale at Old Navy). Don't just pair them with a neutral tee and flip flops. It looks washed out and formless. If you must wear cargo shorts and want to stick to a neutral color, try a safari-inspired look. Find a pocket-happy vest to wear over your tee, and cinch it with a belt for a little spot of color. Jewelry in natural materials and animal print ballet flats add perfect finishing touches without making you look like a big game hunter.
I can't say I'm a fan of cargo shorts, though; the pockets just add bulk in the hips and thighs. I think they're best left for yardwork and camping. A khaki walking short is an infinitely better option for weekend fun. Use your neutrals as a backdrop for color, color, color! Add a colorful scarf or jewelry. You can even switch out your sandals for something brighter.