Late 20's Work Wardrobe

“What pieces are key to building a work wardrobe in your late twenties? Everyone loves a pair of heels, but in my business of sales where I spend a good amount of time on site at construction zones, I have such a hard time finding pieces that work for running around like a madwoman (literally running sometimes), walking cobblestone streets and job sites all day without sacrificing comfort in both shoes and pants/tops.”

— Lauren

While this looks comfy, I'm pretty sure you can't get away with this outfit. Image: http://www.sydneypartypeople.com/profiles/blogs/review-bondi-hardware-s-1st-birthday-party 

Girl, I hear you. I love heels just as much as the next woman, but sometimes they just. don't. work. 

For your specific style question, I am focusing on what will make you the most comfortable while still looking put together AND keeping your ability to walk, sans tottering around on sidewalk cracks and cobblestones. 

Shoes - focus on these flat and sturdier styles that will work with you, not against you:

1. Pointed toe flats. Always, always wear pointed toe flats. This is my style manifesto. They make your legs appear longer, add polish to an outfit, and instantly make you look like an adult (9 times out of 10, just say no to ballet flats for work). 
2. Flat boots. Flat boots (including to the knee or over the knee depending on your work situation and what bottoms you choose) can be a great choice especially in colder months. Avoid excessive details like lots of buckles or rivets and think sleek and slim.
3. Brogues/oxfords/loafers. Brogues and oxfords are similar in look, but think of brogues as the oxford's big brother - they are typically chunkier than the slimmer oxford. Loafers tend to have a slipper look to them, so experiment with what works better for your style and work needs.
4. Thick heeled boot. Sometimes you just need a heel, whether it's for that bit of sexy confidence or maybe your pants are just too long and you haven't been to the tailor. The B. P. Trolley boot from Nordstrom is an internet favorite and it gives you lift without falling over thanks to the sturdy heel.

Bottoms - choose styles and fits that are appropriate for your field. That said, you can wear almost any style.  

1. Cropped pants. Cropped or pants that stop at the ankle are great with almost any of kind of shoe. I love them with flats as well as oxfords and they can even work with boots depending on how slim the pants are cut. Bonus - add heels for date night and your pants are doing double duty.
2. Skirts/dresses (but no minis). Believe it or not, skirts and dresses don't have to be fussy. For your particular work environment, they can be great in fall/winter paired with tights and boots for a different, but fully covered look where you can easily move around. 
3. Bootcut/flares. These types of bottoms can work with flats but look great with the thick heeled boots. The heel of the shoe coupled with the longer pant style will help make your legs look longer (or you appear taller, whichever way you want to look at it).
4. Jeans. It sounds like you have the option of a somewhat dressed down work environment, especially when out on construction zones, and jeans are totally appropriate for that setting! Go for a dark wash so that they can transition to the office or meetings and choose sturdy, flat boots for days when you are also donning a hard hat. 

Tops - tops will largely depend on what you are comfortable with, but as a general rule of thumb, more coverage will most likely equal more comfort for you in doing your job, being active and able move to move around without any, er, slips.

1. High necks. When looking for work tops, consider staying with ones that have a neck that doesn't dip to low, usually in scoop or crew neck styles or a blouse with a slight v-neck. Look for materials that are silky to give an upscale feel to your work ensemble. 
2. 3/4th length sleeves. I love this in between length because it helps provide a little more warmth but can still be worn year-round unlike sleeveless or short sleeves which may look out of place in colder weather.
3. Stripes/prints/colors. You can really play up a work wardrobe by introducing stripes/prints/colors that work for you and your style. 
4. Neutrals + accessories. Others prefer to keep their work outfits neutral but don't forget the accessories. A well tailored jacket/blazer, scarf or earrings can quickly transform your outfit.