If a loaded firearm and/or BUG(back up gun) isn't handy or allowed, there are a few gadgets & devices that could be used in a CQB event or critical incident.
Many savvy license holders & armed professionals carry these items with sidearms too,
OC spray, I have the small Mk III size Sabre Red Crossfire now but I may upgrade to the Mk IV size & buy the Vexor microspin brand from Zarc or Cold Steel's Inferno. Sprays & Mace are not ideal but they can be better than shouting or hand claps.
A tactical white light or flashlight(Fenix, Surefire, 5.11 ATAC, Maglight, etc). The new bright type have strobes(cool way to distract or disorient a attacker) and they can be used to alert security/sworn LE officers in a emergency. New designs are light, compact & long wearing.
A folder knife or small fixed blade. Knives are always handy & can assist you in a critical event(Ka-Bar TDI, Benchmade, CRKT, Blackhawk-MoD, Ernest Emerson, Gerber, William Henry, Cold Steel, Buck, Kase, Stryer, etc). Some like the Spiderco blades, I do not.
Leatherman, Gerber & a few others make Swiss Army type multi-tools. I purchased a Leatherman tool in 1990 & used it often in my armed forces enlistment. New styles are great & have many useful tools.
Finally, I'll add a new tactical item; the defense pen. These run anywhere from $5.00 to $200.00,
. There are many pens with cool gadgets & add-ons but Id use the KISS(keep it simple stupid) method. I do like the Uzi pen with the hidden handcuff key,
. The best well engineered brands that I could buying include the John Williams model by CRKT or the Tuff Writer Operator sterile version(no logos or marks). The type that break auto glass or can tear-rip the skin(get DNA) have merit. Tuff Writer Operator pens look high-speed, low drag & could be great for outdoor uses(job sites, EP details, special events).
The KAMA pen & the Uzi models are good too. I got a Uzi(sharp crown type, grey) for a good friend who does RE/legal work in New York City. He leaves it on his desk,
www.coldsteelarizona.com www.crkt.com www.qmuniforms.com www.policehq.com www.galls.com www.uscav.com www.surfire.com www.thinkgeek.com www.tuffwriter.com www.bladeHQ.com www.blackhawk.com www.williamhenrystudios.com www.ernestemerson.com