i have my first long shift tomorrow, help (AUS)

i started working for mcdonalds 3-4 months ago and tomorrow i have my first shift that is 7 hours long (8-3)

how do i cope with this? i can barely handle a 3 hour shift because i have multiple disabilities affecting my strength, tiredness, awarness, and ability to stand on my feet for extended times.

if i cant handle 3, how do i handle 7?