What things should not be missing in your suitcase? Good question. Next question: In which period are you going to travel to Mauritius?
If you come in the winter season from April/May until September, you will probably have a few short rain showers which usually do not last long and after them the sun shows up again. Do not forget to bring your swimming things, you can enjoy the water for a few days. Apart from that, you bring everything except of a turtleneck sweater. T-shirts, tops, light pullovers and at night maybe a cardigan, if you are planning to do a lot of trips on the island, a rain coat would be a good idea. There is more rain in the south of the island and a shower might surprise you, then it is good to have a rain coat with you. Besides that you should bring flip flops, sneakers and ballet flats which you will probably all wear during your stay.
Summer season is from October until March/April. In those months you will walk around in short clothes for sure. Of course, swimming suits are a must. In January, there can be small cyclones, then it is recommended to have a rain coat with you.
Flip flops are worn by most of the people, but some of them prefer sneakers.
And very important in these months, is to bring sunscreen lotion and after-sun!
Especially when you lay on the beach you are exposed to the sun and need enough protection.