Optical Power Meter, also an RJ-45 coupler and a long patch cord, that way you can go and sit in comfort somewhere while consoled up to switch. Others have mentioned this too but also a good VFL (visual fault locator) if you work with fiber. Make your company pay for these things unless you’re like me and want to take tools with you to the next job, and you do work on the side.
Edit: Adding Snips! Learn how to hold and use them.
Klein Tools 21010-6-SEN Free Fall Snip, Carbon Steel https://www.amazon.com/dp/B00HAN2RRY/ref=cm_sw_r_cp_api_glt_fabc_SY2N7FM7W3FV5VXD32V3?_encoding=UTF8&psc=1
Fluke Networks MT-8200-60-KIT IntelliTone Pro 200 Toner and Probe Kit, IntelliTone Probe and Toner Kit https://www.amazon.com/dp/B00N2S6RPY/ref=cm_sw_r_cp_api_glt_fabc_BD400BK8ZZEQ8NQXGCST
Also Klein makes great tools I carry the following screw drivers: 11-1, a flat head, and a micro 4-1 (all non ratcheting)
Klein Tools 32500 Multi-Bit Screwdriver / Nut Driver 11-in-1 Multi Tool, 8 Industrial Strength Bits, 3 Nut Driver Sizes, Cushion Grip Handle https://www.amazon.com/dp/B0015SBILG/ref=cm_sw_r_cp_api_glt_fabc_C8JX8H7RSA1RAPZ2X0H7
Precision Screwdriver Set, 4-in-1 Electronics Screwdriver with Industrial Strength Phillips and Slotted Bits https://www.amazon.com/dp/B01EOY7LTA/ref=cm_sw_r_cp_api_glt_fabc_TXPYFR74Q7CKJDJTJJGJ
Fluke Networks MT-8200-60-KIT IntelliTone Pro 200 Toner and Probe Kit, IntelliTone Probe and Toner Kit https://www.amazon.com/dp/B00N2S6RPY/ref=cm_sw_r_cp_api_glt_fabc_BD400BK8ZZEQ8NQXGCST
For Tone gen, Fluke makes the gold standard. They also have a cheaper version. You didn't mention a probe, so maybe you are looking for a cable certifier?. That's super expensive though. if you just have to test that there is continuity and not certify the cables, you can use this, or this if you want to look like a pro.
As for Screwdrivers, Wiha makes the best screw drivers, hands down. I have this set for working on electronics & laptop repair. Magnetic tool-kits are fine. This isn't the 80's anymore. There aren't too many magnetically sensitive items inside a computer anymore. especially with the advent of SSD drives.
As for a toolbox, depending the work, I prefer a tool bag or pouch.
Good luck, hope that helps. What helped for me when I started was to go to harbor freight and just get an assortment of tools. As I worked I slowly replaced the stuff I used all the time with quality gear, and didn't have to burn myself buying expensive tools and gear that I would never use.
It's expensive, but you'll only buy it once.