Some Basic Education
You should have some basic education i.e. basic mathematical skills. Ability to count, add and minus things quickly is essential for this job, especially if you are required to listing record of products or an inventory of the stock you have unloaded during your shift.
Ability to Communicate
An ability to communicate with your immediate supervisor is a must. For example, if you are a foreign worker in the US, you should be able to speak as much English so that can communicate with your boss or authorities in case of emergencies. A language barrier can be devastating some time.
You might be required often to handle the stock on your own, without a helper. In such situations you are totally dependent on your judgement. You should have a good judgement, but avoid doing a job if you have a slightest doubt that you can handle it properly.
Knowledge of Health and Safety Guidelines
Handling of stock involves health and safety of workers more than it does in some other jobs. So be fully aware of health and safety guidelines and implement them during all the time and at all costs. For example, do not stop using safety equipment at any time. Also take care of health and safety of other workers.
Ability To Respond in Emergencies
If you have a natural ability to effectively respond in emergencies, it is a great help in doing your job. In case of any accident you should be able to seek help from the relevant departments quickly and manage the situation by yourself as much as you can but do not violate rules in such situations. For example in case of a fire, you give yourself priority in exit to safe place.