As a young engineer, you get a pretty decent amount of shit from some of the older engineers. It's normal for a newbie in any field to get this but step onto the job site where contractors are building your equipment, and it's a whole other ball game.
One of the things that bugs contractors the most is having an engineer (especially fresh out of college whose experience is usually solely theoretical) who has never changed a tire, much less coordinated the construction of a major plant, come up to him and try to tell him how to do his job. My first bit of advice is to speak as little as possible, this provides less opportunity for ridicule. Once you have internalized that, I've got 5 simple tips to make walking onto the job site easier.
First off you will need a hard hat. Whenever you go anywhere that will require a hardhat, they will have them to borrow. Besides the obvious problem with borrowing one, that it might be used by 100 other people who have sweat in it, another problem is everyone will know you borrowed it, it's cheap, you didn't bother taking the time to fit it correctly and it looks awkward.
When you go to buy one for yourself, make sure you steer clear of the fiberglass ones, although they look nice, they are usually reserved for the foreman on site. My suggestion when buying a hardhat is to go with one like the one pictured. General contractors are generally pretty patriotic people (just look at their trucks or websites, the use of American Flags will have you seeing stars and stripes when you close your eyes). As Stephen Colbert has taught us, nothing screams patriotism like American Flags and Bald Eagles. A hat like this will get smiles and compliments from tons of people and will make them warm up to you. This will make discussions with them a lot easier because they will feel like you're one of them. Keep in mind, this is the hardhat you keep in the front seat and polish at the end of the day, not throw in the trunk. Normally a hardhat should be beat and worn but a hardhat like this needs to be cared for and respected.
The Second thing you'll need is Steel Toed Boots. Now I KNOW you will want to cop those titanium-toed boots, or those low top lace-ups. Who wouldn't, they are light and they breathe. The thing is, nobody wears them, you want to go with something more like that on the left. They are simple. they are leather and they do the job. I am not saying you shouldn't find a pair that is comfortable, but just keep the style simple and similar to the others.
Once you have the bought the shoes, I would recommend wearing them around for a while before stepping on site. Once you have water sealed them, rub dirt all over them and then clean it off, I would recommend doing this at least a dozen times (and I mean really work the dirt into the shoe). After you have done this, walk down to your local hardware store and wander down the isles, dropping anything you can find on them: hammers, 2x4's, a kitchen sink, whatever. Once you have done this, you are ready to take em on site.
The next thing you should pick up is a good piar of safety glasses. These should look a lot like sporty sunglasses, not like the ones your dad wore in shop class.
The final tool you will need is a good tape measure. Resist temptations and stay away form the ultrasonic, laser guided or the battery powered ones. The batteries will run out and you will never replace them. A solid, 25' long measure is probably the most you'll need. It's very important that you know how to use this properly. I would practice with this pretty regularly until you are a pro. Go around and measure everything in your house at least 3 times. Measure every crack and crevice. Hell, get your roommate involved and have them ask you to measure random things. You need to do this so when someone on site asks you for a length, you can draw that thing off your belt and slide it into position quicker than they can grab a pen.
My last tip is to take some hands-on classes (welding, shop class, electrical, anything). Stay away from inspector classes. The only thing a General Contractor hates more than "Made in China" is an inspector. You need to have some hands on experience so that you are comfortable out there whether you are handing someone a tool or yanking a piece of equipment apart. The last thing you want to do is giggle when someone asks you to hand them a pair of dikes...