I don't act different when I'm out as opposed to when I'm staying home all, day, but I don't shower every day, either. As for clothes, well I don't wear "outside" clothes when I'm inside (I wear pyjamas, robes, etc the second I get home, and only change to go out) so often I wear them more than once. Especially if I only wore them to go get the mail or something, it seems that if I would have worn them for 8-12 hours otherwise, wearing them 5 minutes didn't ruin them or something.
Now I might sometimes take a shower right before an interview or something on top of what I would have done otherwise (say, if I took a shower the night before, I wouldn't normally shower again in the morning, but I might for an interview) but not just for going out, only for something where my appearance might be very important (for instance get me a job).