First, we need to find the number of students who bring lunch:
1/3 x 36 = 12 students bring lunch.
Next, we need to find the number of students who order lunch:
1/2 x 12 = 6 students order lunch.
So, the total number of students who eat lunch each day is:
12 (who bring lunch) + 6 (who order lunch) = 18 students.