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Before you go on a site visit it is important to make sure you have all the tools and materials you may need out there. The last thing you want is to be on site and not be able to get all the information you need because you don't have the proper equipment. 

I do a lot of site visits so I typically keep all this stuff in the trunk of my car. You can keep it in your office in a box if needed, but it is nice to have it ready to go at all times.

Here is a quick list of things to have with you when you do a site visit:

Keys to the site
    
You don't want to arrive on site only to find a locked gate. Call the owner and make sure access will be provided.

Orange or yellow safety vest
    
You want to be seen at all times while on a construction site. Don't leave home without a safety vest.

Hard hat (brain bucket)
    
You MUST protect that money making brain of yours. Always wear a hard hat when on site. I know of a person who didn't wear a hard hat because there was no construction going on above them, only to have a tree branch break from high winds and hit them on the head.

Steel toe shoes
    
Although they are small, toes are important. Make sure you invest in some good steel toe shoes that will last. I find that boots are best.

Digital Camera
    
Take more pictures than you think are needed. There have been countless times when I got back to the office and wished that I had taken more pictures.

Full or half size set of plans and specifications
    
Bring a set that you can mark up with anything you find onsite. Do not take originals. Originals should stay in the office for safe keeping. Construction sites are sometimes unpredictable and plans can get damaged.

Site visit checklist or inspection log
    
Be sure to write down everything you need to see while on site. Do not rely on your memory.

Measuring tape
    
To measure stuff.

Pocket scale
    
To measure stuff on the plans.

Flashlight
    
You may need to look down a manhole or at the understory of a house. A flashlight will enable you to do this with ease. Fiat Lux!

Orange cone
    
To protect you and your vehicle when out in traffic.

Proper clothing for weather and site conditions.
    
A suit is not normally a good choice when going to a construction site. I keep a change of clothes at the office just in case I'm dressed to fancy on a day that I didn't expect to visit the site.    

Pen and or pencil
    
To write with.

Cell phone with important numbers i.e. client, foreman, office
    
You may need answers quickly and you want to be prepared.

Pocket knife (never know when this is going to come in handy)
    
Contractors can get out of hand sometimes and it is nice to have a backup plan if things go sour. JUST KIDDING! Contractors are great (Most of the time).

Clipboard
    
To put all your papers on.

So what do you think did I miss anything?