You'll always find the first few days/weeks rather difficult.
You'll get sore etc. - I still do, after nearly a year of working at the same place. ^^
Kinda sounds like a fun job, to be honest. At least to me. xD
I guess a supermarket could be 'easier'. However, there, you probably need to count on heavy work.
Such as lifting, pulling, pushing.
Perhaps not too much, but it still happens.
A lot of walking and stress.
'Course, I've only worked in a smaller shop but eh.
I do stock work at the hospital in my city.
Requires a lot of heavy lifting, and math.. I hate math.
Basically, we make sure the wards at the hospital have towels, pillows, blankets, underwear etc.
As well as the people who work there and students.
Answering phones/mail, helping the customers.. (Not always fun at all.)
Making sure the robot has enough clothes, that it works etc.
(A system we have for the people who work at the hospital.)
Cleaning. T_T