You can apply for a free Member+ rank and receive the /echest command. This gives you a virtual ender chest and allows you to carry more inventory. You can use "/member " in game to be taken to the web site where you can request it.
Plus, Backpacks are a mod, which would take a while to download, Cause lag and maybe the server be down for some time, So either get Skyblock VIP or Member+ for /echest
When you are a donator I believe that you can do a command like /pv 1 to get a portable double chest. although im not sure on this because I don't usually play on factions or skyblock.
