If I wanted to build a mostly-portable-but-still-comprehensive kit to use in emergencies, either my own, or simulated ones through ARES or RACES, what should I put in the kit?
If you are active in ARES or RACES, they will support served agencies. The potential needs of these agencies and your role within the organization will determine the contents of your go-kit. My local ARES has a field operations manual that includes two levels of go-kits for the average member. The go-kit and your skills get tested and refined through regular drills, simulations, and desk-top exercises. We also update our field manuals based on the lessons learned from these drills.
Your Role
You can imagine that if your role is to staff an EOC (Emergency Operations Center) or a Comms Trailer, your go-kit might be rather sparse - probably an HT and your personal effects. On the other hand, if your role is to provide comms support for your local SAR (Search and Rescue) team, your go-kit might be rather extensive including the ability to deploy cross band, hill top radios, for example. In my case, my go-kit is actually a go-truck as I have state wide responsibility to provide technical assistance in the event an emergency. I have spare repeaters, antennas, RFI kits, AC and DC distribution systems, a spectrum analyzer, technical reference manuals, etc. that get loaded into the truck based upon the needs. Clearly this go-kit is different from most people's idea of a go-kit. The point is knowing your role is the key to stocking your go-kit.
Deployment Location and Duration
The location and duration of your deployment has a profound impact on the contents of your go-kit. Most of us could comfortably operate for 8 hours or so with just our technical gear. Beyond that, issues such as personal hygiene, F&H (Food and Hydration), sleeping gear, etc. start to come into focus and must be addressed in the go-kit plan or in the site logistics plan.
The duration and location can also impact the power requirements of your portable/mobile operations. If your assignment is to do police or fire ride-alongs for support comms, do you have the right gear to plug into the vehicle power and to deploy an antenna on the vehicle? Your stack of batteries may only last for a few hours and then you may find that your cigarette adapter cord isn't usable because all sockets are already taken or at capacity. On the other hand, if you are providing comm relays for a wild fire team, your nifty solar panel may not be at all practical since the sun is too obscured by smoke.
Practice
Hopefully your ARES/RACES team conducts a couple of drills a year to test the environment, your skills, and your gear. This also helps to understand the served agency's command structure, their terminology, their temperament, and the type of comms they really need (perhaps contrasted to what they asked for). It also gives them a chance to experience your capabilities and expertise.
Practicing with the served agencies may also highlight unanticipated issues. For example, many are surprised when their trusty $40 Chinese HT is rendered completely useless in an RF dense environment like an EOC. The lesson learned may be that a different radio is needed for the go-kit.
In the absence of organized practice drills you should, at the very least, setup your gear in the envisioned field conditions and try operating it for the duration you anticipate being deployed. This not only enhances your skills, but it will test the readiness and completeness of your gear. It is usually the basic things that get overlooked - things such as flashlights, pens, communication forms, frequency charts, a comfortable chair, headphones, medications, contact supplies, etc. that are not thought of in advance but become painfully obvious with realistic practice and drills.
Laptop with programming cables for radios
While at first glance, this would could fall under the category of "be prepared", I would cynically view this as a red flag indicating lack of preparation. Today's radios typically have a hundred or more memories in them. With proper planning, the radio can be programmed in advance for most scenarios. For example, our ARES field manual has all of the frequencies listed for all repeaters in our county and all adjoining counties. The list includes simplex, reverse repeater pairs, and predetermined cross banding frequencies. We regularly offer programming of radios with this list at our meetings. Our field manual also includes all FRS, GMRS, MURS, NWS, and served agency frequencies.
While the laptop could prove helpful, is there other gear that could take its place that would be more effective in helping you to carry out your role?
Identification
Emergency situations generally involve restricted access to certain locations. You must have the right identification with you to gain access. Your served agencies will facilitate gaining the proper credentials including recognized photo ID cards. For unanticipated issues, having your passport, drivers license, and a copy of your FCC license(s) may be helpful.
Grab Lists and Refresh Lists
While a basic go-kit can be prepared in advance, many times there are things that need to be grabbed at the last minute. Examples include medications, snacks, identification, or a generator and gas can. A list that is prominently attached to your go-kit can help you to avoid forgetting these items "in the heat of the battle". Force yourself to check-off items on the list as they are packed if your list includes more than a few items.
You can also use a grab list to enhance your go-kit for longer or different deployments. The grab list could include the items needed to expand your day go-kit to a three day go-kit, for example.
Several items in your go-kit may have expiration dates and should be replaced or refreshed on a periodic basis. Examples include alkaline batteries, bottled water, snack bars, hand warmers, and gasoline. Keep a "refresh" list of these items along with a "replace by" or "do by" date. Take this list in hand once a month and check for anything in need of attention. Don't forget to include charging rechargeable batteries on this list as well as periodic maintenance items such as generator start-up and test, oil changes, updating programmed frequencies, etc.
The Family
Emergency deployments usually involve leaving the family behind while you go on your assignment. Don't overlook their own safety/security and their concerns about your safety while you are deployed. Your go-kit should include plans and capability to communicate with your family. They should have a complementary plan accessible to them at home so they know how they can get in touch with you. Don't forget to practice this plan with them as well.