Keep in mind this was in the Darkness Falls mod which always had 10 slot bars. This worked well for me in that mod so I probably won't change it up too much for vanilla. In vanilla I'd probably take out one of the guns and replace it with a healing item cause I wouldn't be speccing into every tree but DF brings back the "learn by doing" system.
1.) Axe
2.) Pick
3.) Shovel
4.) Melee 1 (sledgehammer)
5.) Melee 2 (stun baton cause I like being able to stun tougher enemies)
6.) Stealth weapon (bow/crossbow, sniper, etc)
7.) Pistol
8.) Machine gun
9.) Shotgun
10.) Harvesting tool/knife/frames
Now the DF mod is increasing their toolbelt to 15 and tbh I think that's too many. I've got 13 slots figured out (gonna add in a healing item) but I have no idea what I'll use for the last 2.