[SKB_Hamsters]

This is something which comes down to personal prefference really - it not necessary to add but to me it does no harm if the nutritional values are almost the exact same (I.e. Harry Hamster and Science Selective)
I personally prefer to add a pellet food to the Harry hamster food - as my Syrians have been a bit picky and will leave some pieces so aren’t getting the complete balance of nutrients - therefore I like to mix in the science selective hamster pellets in which my girls seem to quite like (so use them as treats too!) to ensure they are getting all the nutrient they need.
Plus Liquorice seems to prefer the science selective pellets to the Harry Hamster food so will eat her pellets first before eating the rest of her mix!

Serendipity has given so very good recommendations also on what else to feed. Also I too would recommend the rosewood natural treat sticks these are a fond favourite of my hammies.