Supplies COVID test to myself and sick son (7)
I believe the answer is:
'supplies' is the definition.
'to myself and sick son' is the wordplay.
'to' becomes 'rat' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'myself' becomes 'I'.
'and' says to put letters next to each other.
'sick' indicates anagramming the letters.
'son' with letters rearranged gives 'ons'.
'covid test' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for rations that I've seen before include "Limits (supplies)" , "fixed allowance" , "Food as issued" , "Food allowances" , "Fare" .)