In the ammobox initialization line:
null = [this] execVM "virtual_arsenal_init.sqf"

In virtual_arsenal_init.sqf:
//Init stuff
_crate = _this select 0;
["AmmoboxInit",[_crate,false,{true}]] spawn BIS_fnc_arsenal;

//Lists of items to include
_availableHeadgear = [
    "rhsusf_ach_helmet_headset_ess_ocp",
    "rhsusf_ach_helmet_ocp",
    "rhsusf_ach_helmet_ESS_ocp",
    "rhsusf_ach_helmet_headset_ocp"
];

_availableGoggles = [
    "G_Shades_Black",
    "G_Shades_Blue",
    "G_Shades_Green",
    "G_Shades_Red",
    "G_Spectacles_Tinted"
];

_availableUniforms = [
    "rhs_uniform_cu_ocp"

];

_availableVests = [
    "rhsusf_iotv_ocp",
    "rhsusf_iotv_ocp_Repair",
    "rhsusf_iotv_ocp_Grenadier",
    "rhsusf_iotv_ocp_Medic",
    "rhsusf_iotv_ocp_Rifleman",
    "rhsusf_iotv_ocp_SAW",
    "rhsusf_iotv_ocp_Squadleader",
    "rhsusf_iotv_ocp_Teamleader"
];

_availableBackpacks = [
    "rhsusf_assault_eagleaiii_ocp"

];

_availableItems = [
    "ItemWatch",
    "ItemCompass",
    "ItemGPS",
    "ItemMap",
    "ItemAndroid",
    "Rangefinder",
    "NVGoggles",
    "NVGoggles_OPFOR",
    "NVGoggles_INDEP",
    "Laserdesignator",
    "tf_anprc152",
    "rhsusf_acc_anpeq15",
    "rhsusf_acc_anpeq15A",
    "rhsusf_acc_ACOG",
    "rhsusf_acc_ACOG2",
    "rhsusf_acc_ACOG3",
    "rhsusf_acc_compm4",
    "ItemcTabHCam",
    "ItemcTab",
    "AGM_M26_Clacker",
    "AGM_Clacker",
    "AGM_DefusalKit",
    "AGM_EarBuds",
    "AGM_CableTie",
    "AGM_MapTools",
    "AGM_Vector",
    "AGM_ItemKestrel",
    "AGM_Altimeter",
    "AGM_Morphine",
    "AGM_Epinephrine",
    "AGM_Bandages"

];

_availableMagazines = [
    "rhs_mag_30Rnd_556x45_Mk318_Stanag",
    "rhs_mag_30Rnd_556x45_M855A1_Stanag",
    "rhs_mag_30Rnd_556x45_M855A1_Stanag_Tracer_Red",
    "rhs_mag_30Rnd_556x45_M855A1_Stanag_Tracer_Green",
    "rhs_mag_30Rnd_556x45_M855A1_Stanag_Tracer_Yellow",
    "rhs_mag_M433_HEDP",
    "rhs_mag_M4009",
    "rhs_mag_m576",
    "rhs_mag_M585_white",
    "rhs_mag_M661_green",
    "rhs_mag_M662_red",
    "rhs_mag_M713_red",
    "rhs_mag_M714_white",
    "rhs_mag_M715_green",
    "rhs_mag_M716_yellow",
    "rhsusf_100Rnd_556x45_soft_pouch",
    "rhsusf_100Rnd_762x51",
    "rhs_m136_mag",
    "rhs_fgm148_magazine_AT",
    "DemoCharge_Remote_Mag",
    "SatchelCharge_Remote_Mag",
    "RH_15Rnd_9x19_M9",
    "SmokeShell",
    "SmokeShellRed",
    "SmokeShellGreen",
    "SmokeShellYellow",
    "SmokeShellPurple",
    "SmokeShellBlue",
    "SmokeShellOrange",
    "AGM_HandFlare_Green",
    "AGM_HandFlare_Red",
    "AGM_HandFlare_White",
    "AGM_HandFlare_Yellow",
    "AGM_M84",
    "HandGrenade",
    "MiniGrenade"

];

_availableWeapons = [
    "rhs_weap_m4a1",
    "rhs_weap_m4a1_grip",
    "rhs_m4a1_m320",
    "rhs_weap_m240B",
    "rhs_weap_m249_pip",
    "rhs_weap_M136",
    "rhs_weap_fgm148",
    "RH_m9",
    "Binocular"

];

//Populate with predefined items and whatever is already in the crate
[_crate,((backpackCargo _crate) + _availableBackpacks)] call BIS_fnc_addVirtualBackpackCargo;
[_crate,((itemCargo _crate) + _availableHeadgear + _availableGoggles + _availableUniforms + _availableVests + _availableItems)] call BIS_fnc_addVirtualItemCargo;
[_crate,((magazineCargo _crate) + _availableMagazines)] call BIS_fnc_addVirtualMagazineCargo;
[_crate,((weaponCargo _crate) + _availableWeapons)] call BIS_fnc_addVirtualWeaponCargo;