Many items have been removed or changed. Lots of new items, all the way up to level 40, are available from vendors and as loot.
If upgrading from a previous version, you'll receive voucher credits for any of your items which were removed from the game. You may redeem these credits for upgraded items at most friendly stations.
Ammo is no longer an inventory item, and specialty ammo effects are now weapon properties. Most weapons no longer scale with player level, so keep your eyes open for upgrades! Many of your previously equipped items may suddenly feel underpowered, due to being underleveled.
If you were in the middle of a scenario and aren't able to upgrade right away, consider equipping your emergency weapons. They have been upgraded, will scale to your level, and should allow you to get by until something better comes along.
The game manual and ZigDB have not yet been updated to reflect these changes. Will get to that ASAP.