In reply to Danylblack4:
Map and compass. I also have OS Locate ( https://www.ordnancesurvey.co.uk/shop/os-locate ) on my phone, which gives you your 6 figure grid reference. I think the combination of these three is a good use of old and new technology.
I have Viewranger on my phone too and sometimes use it, but to track where I have been than as a navigation aid.
I don't stay in touch with the outside world when I'm walking but most of my walks are day walks . However, even for day walks I always let some know in reasonable detail where I am going.
I don't know of any useless gear, but I have never found, in the UK, the need to have an altimeter.
Dave