You have 3 items in the 1st category  (meat);
         2 items in the 2nd category  (vegetables);
         2 items in the 3rd category  (salads);
         2 items in the 4-th category (dessert).


if you choose one item from each category,then, 
according to the Fundamental counting principle,
you may have 3*2*2*2 = 24 different dinners.


So, during 24 days, you may have different dinner.


So, 24 days you may eat different dinners, but on the day 25th you inevitably will eat the same dinner second time.


ANSWER.  At most, there are 24 days before you will eat the same dinner second time.