Dear student,
There are different types of plastics, so depending on their use plastics can be substituted by some other materials. Currently some biodegradable or bio plastics are also available in the market.
Some common substitutes of plastics are-
1) Paper
2) Wood
3) Metal
4) Glass
5) Cloth
So, we can say that those substances can substitute plastics that are durable, non-reactive, and should not contaminate the environment.
Regards