It is very unlikely that bears or porcupines will bother you if you keep a clean camp. Sanitation is a serious issue. Do not wash your hair or dishes in the streams. Use public restrooms if you are camping near town. Treat or boil all drinking water, or get it in town.
Fires are fine down on the beaches, but they scar the fragile alpine environment.
Don't build fires above the treeline. Downtown you can get your clothes clean and take a shower at the Harbor Washboard, about a block north of the Juneau end of the Douglas Bridge. There's a coin laundry in the valley at Mendenhall Mall next to Super Bear grocery store. It's located next to the high school, also a few blocks from the north end of the Douglas Bridge. Schedules are located behind the driver's seat, just jump on and grab one at a bus stop.