Does your phone have a replaceable battery or a built in one? If it is replaceable it might be worth getting a new one and maybe a spare. Also you say it barely lasts for a two hour ride. Are you turning off the phone and wifi function? Searching for a signal really sucks battery. I find that putting my phone in airplane mode makes the battery last several times as long especially if the signal is sketchy or non existent.
I have never bothered with a horn or bell, but I can yell really loud
How much lock you need may vary with the locale and how careful you are about where you leave your bike. I use the cheapest lightest cable lock I could find. I think it weighs 5 ounces. In places where I am concerned I don't leave my bike unattended. I sometimes have wheeled it up and down the aisles of a store. On the other hand in a lot of places where I tour I don't bother locking at all.