If you had sex within seven days of not taking the pills, there is a chance of pregnancy.
But the light period could also be due to missing the pills. Did you have any spotting during camping while you weren't taking the pills? I would take a test now to ease your mind and just wait for your period to come.
And no, your period won't always come on the first day of the placebo week.
If you extend your placebo week (meaning you were taking it on Sat and now you switched to Sun) you also have a risk of pregnancy until you have been taking your pills for a week.
But a late or lighter period is pretty normal. You can always test if you're worried.