Just like real estate, it's all about location and timing.

If you are in deep backcountry off-trail, a PLB is a great idea. If you're on a busy trail in peak hiking season, maybe not so much. In between is a sliding scale.

I spent Wednesday on the Appalachian Trail doing some volunteer trail work (and getting paid because I have a cool employer). I was on one of the more remote sections around here, in the center of a 12-mile long, 4000' high ridgewalk with no road access, meaning it's a stiff climb and a long stroll to get up there no matter which way you go.

In the 8 hours I was up there alone painting blazes, seven backpackers and one hunter walked by and stopped to chat. There are rural roads that don't get that much traffic. A PLB, for me, in this area, is too much. Your mileage may vary.

Likewise, I don't bother with a signal mirror or sunscreen (tree cover limits both) or bug spray (no bugs). However, I usually have two whistles and I'd add a first aid kit to the list above. If you are in AZ, your situation is very different than mine and as you gain solo experience you'll adjust your gear accordingly.

Lots of other good suggestions here already. +1 on the leaving a plan with someone. The Lovely Spouse always gets a list and map from me: a) parking HERE, b) coming out HERE2, c) at this TIME (with a hefty safety cushion, like half a day, for usual delays). If I'm not home by TIME2, call 911 and ask for THIS SAR team, sheriff, etc. appropriate for the area.

My final suggestion is to take a book. Exploring solo is great, but unless you are used to twenty-four hour solitude there may be times you feel bored.