It is a great looking custom pack. For approval, however, there are specific guidelines for what the pack is supposed to look like:
http://www.501st.com/databank/Costuming:TK_hwt
Backpack For 501st approval:
Styled after the ANH Sandtrooper packs or a simplified pack as seen in the video game (Battlefront series). For level two certification (if applicable):
Backpack should be lightly scuffed,(battle worn), but not weathered like a Sandtrooper (TD). For level three certification (if applicable):
If an ANH style Sandtrooper pack is used, it shall have the appropriate details for a specific ANH Sandtrooper, which is being referenced, but shall not be weathered like the ANH Sandtrooper, but lightly scuffed,(battle worn). If a game style pack is used, it shall closely match the simplified pack as seen in the video game (Battlefront series), but shall not be weathered like the ANH Sandtrooper, but lightly scuffed,(battle worn).
It will be great to troop with at a non-canon troop though.