Some of my favorite tips:
On hot days (or any day, really), the Selig Experience in the LF corner on the 200 level is a nice break from the game, a bit of Brewers history and, maybe most importantly, air conditioned.
You can bring in almost anything food and drink wise, except alcohol.
Lots of history to see around the outside of the stadium.
There is a plaque in the brewers 1 lot, marking where #755 landed.
There is the original home plate from County Stadium, along with a monument to the 1950's Braves just north of Helfaer field.
The Brewers Wall of Honor is on the 3B side wall, near the LF corner entrance
The Brewers Walk of Fame is around the OF concourse outside the stadium