Deathwatch Teams equip themselves and operate in ways that are somewhat similar to modern Special Forces groups the world over, in fact I wouldn't be suprised if that was one of the orignal sources of inspiration for the Deathwatch rules in tabletop 40K. Individual squad members get their pick from a wide variety of weapons and kit to suit their skillset and personal preferences.
I assume there will be a system for getting better gear similar to the Wealth and Influence systems used in Rogue Trader and DH: Ascention, but there are plenty of items we can realistically expect to be included. Besides the obvious starting gear (Astartes Power Armor, Chain and Bolt Weapons all round), I'd expect each squad member will also have a limited number of choices/picks/purchases/etc from the entire Space Marine Armory at character creation (although it's unlikely Terminator Armor and Terminator-Only equipment will be included in the core book, and that top-end items like fields, rare artifacts and advanced heavy weapons will be unavailable at creation), including support gear like Auspexes and Teleport Homers.
As for weapons and defensive gear, there's no reason to believe that any weapon from Codex: Space Marines will be omitted from the Deathwatch book, though I expect some of the chapter specific kit will be witheld for use in supplements, you can expect all the standard Bolt, Plasma, Melta and Flamer weapons (In all their Basic, Heavy and Pistol forms) to be there as well as Grenades, Combi-Weapons, Iron Halos and Rosarius, Combat and Storm Shields, Astartes-grade Augmetics and melee weapons such as Mono, Chain and Power Swords, Relic Blades, Thunder Hammers and Lightning Claws.
Another thing you can count on is Special Bolt Ammo, one of the defining characteristics of the Deathwatch is that they have special Bolt rounds for pretty much every kind of Xenos and every kind of situation. Aside from the various types of ammo used by the Deathwatch and Sternguard on the 40K tabletop, we might be lucky to find Ulysses Homing Beacon Rounds and perhaps even Ultramarines Odyseus Psy-Active Tracking rounds.
In short, I'm pretty sure you can just go nuts.