Another solo female traveler here.
Of all the items and suggestions, the only thing I do is put a chair against the door in such a way that it will wedge against entry or make noise if someone tries to open the door. I've lived, traveled and camped alone, in the US and Europe, off and on since my first job out of college in 1967 when I was 21. There's always a chance that something could go wrong, but so far I've been lucky, I guess. Now at 76, I'll be considering some of the suggestions being made.
One thing that always puzzles me is why people carry wallets at all when traveling. I don't carry enough (total of 9) card-like things on trips to need a wallet. At home I regularly carry 22 card-like things in my card holder. I don't really have a wallet anyway. For me, putting all the important stuff in a single place like a wallet or purse or daypack is just asking for trouble.
My first trip to Europe was in 1977-78. It was about 4 months. One travel tip that really stuck with me was to not put my traveler's checks all in one place, but rather in different places so that it would be less likely for them all to get stolen at once.
That probably has something to do with my propensity to wear a money belt like the StashBandz, wear pants with zipper pockets, wear coats or jackets with interior pockets, wear a small, cross-body purse that won't hold much and to leave anything I don't really need back in my room or apartment in a decent safe or hidden in my luggage.
A friend from work traveled a lot to Europe. She would take her normal heavily laden purse, with everything she had in it back in the USA. That worked okay for her -- until it didn't. She was sitting at a group dinner with her purse under the table at her feet. When the meal was over, she realized it was gone. Everything was in it, including her meds and well-identified room key.
By the time she got back to her room and was let in, the thieves had already ransacked the place and taken anything of value. Fortunately, that didn’t include her passport or meds. I'm not sure about credit cards.
In Lisbon, my husband and I saw the guys working the main drag in the center of town. As a younger male was walking facing us, he handed off a wallet to the guy in front of us walking the same direction we were. Blatant and obvious. The wallet was a man's, folded and bulging with its contents. My guess is that it was easily picked from a hip pocket.
On arrival in Rome, an escalator was suddenly stopped by some young men at the bottom who appeared to be having fun fooling around. You already know the rest. I'm sure some folks in the pile up at the bottom lost some valuables. We were at the top just about ready to get on when that happened, so we stepped over to another escalator and avoided the crowd.
There are lots of ways to both increase security and make us feel safer. What works for one person could be too little or too much for another.