When my oldest was 3 I was struggling with some behavior issues as well. I started a chart and tackled one behavior at a time. If he did well for that particular behavior, he earned a sticker on his chart that day. Once he had 3 days of good behavior, he earned a trip to someplace he liked to go (we live near a free zoo, a train store with play tables he likes, a trip to the park, etc.). That way he was getting a reward, but it wasn't a tangible/material thing, rather a special time with Mom - but something HE picked and wanted to do (we did bring his brother too - so it wasn't exclusive 1 on 1, but that would have been good too). Then, once we had a few reward days for he behavior we were working on, then I switched the chart to be for the next thing we wanted improvement... and the other behavior was expected to be better from that point forward. He understood that expectation because we were doing just one behavior at a time.
I think 5 days might be too long for a 3 year old. And, a whole day might be too long too, maybe break it into two (morning smile/afternoon smile).
I've tried having a prize bag with dollar store treats for improved behavior but haven't found it particularly affective in changing behavior for my 3 or (now) 4 1/2 year olds. I prefer to have a the reward be an outing. That's just what works for us.