It all depends what location you are working at. The (regional) Business Units are more formal, but the Market Units and warehouses are more casual. For the most part, it's business casual. Suits for meetings and any travel. Sometimes they have 'dress down' Fridays. No shorts. Occasional dress down days allow jeans. Never sneakers, shorts, or sandals. Be on the conservative side till you see how others dressed.
Your day usually starts at 8/8:30am. Having worked in a Business Unit, it's very competitive, formal, and political. I didn't know it till I was there. They have very high turn-around. I've worked with great people- all departments and keep in touch. The biggest challenge is being able to tough it out and be available 24/7.
The environment revolves around the department you work in. Sales department is less formal, more friendly. They have better hours, but they have to be ready to take a call/email any hour of the day and travel all the time. It's tough if you have a family or other commitments in your life.
If you're in Finance or Accounting, don't expect a 9-5 job. Typical days are at least 10 hours. During quarter closes, plan on 14-16 hours a day. It's not demanded, but expected. If you don't comply, you'll get written up and let go. I've seen it happen several times. Also, since their sales-focused, they don't pay as much for accounting/finance personnel.
Pluses: Benefits kick in the day you start, which is rare these days (though it may be months till you get an insurance card). You have both a mid year and annual review (only annual are you eligible for salary increase).
Minuses: Health Insurance benefits stink. It's out of New York (even if you live in another state). High ($30) copays. Basic vaccines are not covered. Last year, they got rid of the Pension Plan for new hires. Their 401K plan is not that great, either. You have to tough 5 years out before the good perks