Use only textiles made of cotton, wool or linen (I recommend linen in summer and wool in winter, since cotton isn't very good at conserving your body heat), look for a bamboo toothbrush, avoid foods in plastic packaging (this can sadly be difficult) and only put them in ceramic, metal or glass containers.

I assume your goal is to minimise the amount of microplastics inside your body, so the materials that touch your food are a priority. The amount of microplastics in your food or drink also depends on how long they are in contact with plastic. For example, if you have juice in a plastic bottle, drinking it right away or putting it in a plasticless container would probably result in less microplastics than storing it in the said bottle.

If you are more concerned about nature, try shopping at second-hand stores.