// Du brauchst ein Interface welches deine beiden Models implementieren um eine gemeinsame List zu machen
public interface Buyable {

}

public class DrinksSelection implements Buyable {
	...
}

public class ShishaSelection implements Buyable {
	...
}

// In deiner Warenkorb Activity holst du dir alle shishas und drinks und fügst die in eine List vom Typ Buyable
// und gibst die dann deinem Adapter
// List<Buyable> list = new ArrayList()
// list.addAll(shishas)
// list.addAll(drinks)

public class MyAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {

	private final int DRINK_TYPE = 1;
	private final int SHISHA_TYPE = 2;
	private List<Buyable> list;

	public MyAdapter(List<Buyable> list) {
		this.list = list;
	}

    class ShishaViewHolder extends RecyclerView.ViewHolder {
        ...
        public ShishaViewHolder(View itemView){
        ...
        }
    }

    class DrinkViewHolder extends RecyclerView.ViewHolder {
        ...
        public DrinkViewHolder(View itemView){
        ...
    }

    @Override
    public int getItemViewType(int position) {
        if (list.get(position) instanceof DrinkSelection) {
			return DRINK_TYPE;
		} else {
			return SHISHA_TYPE;
		}
    }

    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
         switch (viewType) {
             case DRINK_TYPE: return new DrinkViewHolder(...);
             case SHISHA_TYPE: return new ShishaViewHolder(...);
             ...
         }
    }

    @Override
    public void onBindViewHolder(final RecyclerView.ViewHolder holder, final int position) {
        switch (holder.getItemViewType()) {
            case DRINK_TYPE:
                DrinkViewHolder drinkViewHolder = (DrinkViewHolder) holder;
                ...
                break;

            case 2:
                ShishaViewHolder shishaViewHolder = (ShishaViewHolder) holder;
                ...
                break;
        }
    }
}