Underground railways in the USA and elsewhere typically use DC supply at around 600 to 800 volts.
There is no cheap simple and compact device to test for DC voltage.
Non contact testers for AC voltages up to about 1000 volts are available, but WONT DETECT DC VOLTAGE.
The ONLY WAY to detect DC voltage is by an approved tester that uses a meter or a lamp connected between the conductor rail and ground.
And even if you DO carry such a device and are trained in its safe use, it only proves that the live rail was dead WHEN TESTED and does nothing to prevent it being re-energised.

The only safe advice is to avoid going on or near the track of an electric railway. If a serious emergency makes going on the track unavoidable, then do not step on or touch any rail, nor allow anything that you are carrying, holding or touching, to touch any rail.

There is no like button on this forum, so, there: like.

Oh my! I've missed that it's a DC entirely! So, my pen detector is useless for that.

Amen.

A friend of mine was a Civil Engineer employed by the Port Authority of NY- NJ. Often, as a junior engineer, he worked supervising the PATH Train ( read "subway") repair crews. He told one story about the explicit testing protocol he was supposed to use to insure the 3rd. Rail wasn't energized, before work began. Well in the middle of his test, one of the older workers got impatient and said the equivalent of, " Look kid, here's how it's done." He then stood back a way and threw a metal bladed shovel at the 3rd. Rail. If it doesn't short and send the shovel flying, he said,it's not "Hot".. I'm not recommending that technique to anyone. But, I always found it an amusing story.

in the early 70's I was stationed in Japan and the Philippines, took some leave time in Hong Kong and Taipei, and TDY to Thailand and Okinawa...once down in SEA, a Thai elephant hide money belt was pretty much universal for the guys in my unit.... a copy of orders with TSCW clearance so you could get on a space available flight, and in the days before widespread copiers, a microfiche type 35mm photograph of your birth certificate to get you into a US Embassy or Legation if you lost your military ID... inexpensive nylon money belts are available similar to this one by AeroStitch...

information and walking shoes.

+1 to paper maps, bus schedules, cab company phone numbers, compass

And shoes you can hike in. Keep spares in the car

A wee bit of an extension of this thought: I keep a file on each state that I add to as I happen to come across an interesting news article, maps, freebies advertising booklets for that state. I also keep motel directories, AAA tour guide books, etc, etc. it's an old 4 drawer file cabinet.

cash is good too.

The world is going cashless. All you need is a credit card and a Starbucks gift card with enough balance for a Latte' and one of those wraps.

Says the guy who can always justify hitting the ATM one more time. Ask me why my credit history sucks...