These solutions are not meant to squeeze out the last bit of accuracy to get a place mear the top on a leaderboard. Instead they provide some exploratory data analysis and compact ML models. They might be of interest as a starting point for your own experiments.

Flavours of Physics (solution) (challenge description)

Costa Rican Household Poverty Level Prediction (solution) (challenge description)

Loan Charge-Off Prediction (solution) (challenge description)