Hancox, who has made 18 first-team appearances this campaign, has been offered a two-year contract with the option of extending his stay for a further year, while Reilly, also a regular under manager Lee Clark, has been offered a 12-month contract extension.
Packwood, who is sidelined after breaking his leg in January, has been offered a one-year extension along with Bell, who has the option of extending his new one-year deal by a year.
Clark told the club's official website: "I have made no secret that the emergence of so many young, talented players in and around the first-team this season has been one of the highlights of my first year at the football club.
"The fact that these new contracts have been offered proves that, as a club, we are committed to building for the future and furthering the development of these rising stars.
"Callum and Mitch have proven to be vital members of my first-team squad this season, as was Will before his horrific injury and I'm delighted to see that he's well on the road to recovery.
"I am looking forward to continuing my working relationship with all three players, while Amari'i is another undoubted talent who both myself and the coaching staff look forward to nurturing."