The toolbar has been fairly rock solid since the very early versions of Photoshop with only additions from Adobe added to the set or perhaps even the occasional item being deleted or shuffled around or added to below another item. Well, that has now all changed and you can edit the tools in 100s of different ways. This does mean that following any tutorials referencing the brushes, shapes etc will all be a lot more confusing as there will probably be no default setting for this central area of tools. Everyone can change the icons and everyone will have their favorites and the features they never ever use. So now if you only use the custom shape tool and the brush tool you can leave those in the toolbar and all the rest of the other items in the extra and that is really useful as the other tools can sometimes just get in the way of the creative process. OK, how to start.
Go to the edit menu and toolbar or go to the box itself and to the bottom and select the little '' and expand out and you will see the edit command there. Probably easier to go to the edit menu as that will always be available. You will then see the dialog for the customize. The dialog is split into three sections with the items in the current setup in the left (default ones or the ones that you have already decided are your favorites) and the ones in the extra tools section are on the right of that (these are the tools that you probably never use) and a selection of buttons to restore defaults etc. There is also a selection of other controls along the bottom such as show the dots (extra tools).
These are the tools that you use a lot. The items that you use that often can go into the extra section. You can now move the tools from the left to right section and right to left. You can move the individual items up and down the left and the right sections so if you decide you want the custom shape at the top of the panel then select it and remove it from the rectangle group and move it up above the current top item leaving a little gap so it does not join the current top group. If you want the selected item to join the group then just place it on the group and it will be added to that and you can place it at the top of the group or in the middle etc just by careful placement of the item. You can do the same in both sections and you can as mentioned, drag them from toolbar to the extra section or back again. As you pass over the various icons in the panel, a thin blue line will appear
You can move individual items and you can move an entire group so say you have the lasso tool and the dodge tool and the burn tool together in a single group and you want to move that into the same group (so it would have to be expanded) then you can select the whole group by passing over the edge of a group and not the individual items and then select that and drag to another part of the set (again, left or right sections)
Now you have all the tools in that you use a lot in their particular places i.e. move tool, custom shape, brushes, rectangular marque tool etc and all the rest such as the note tool in the extras section what happens now. If you click the done then you can leave and go back to the toolbar and select the ones you want to use and you will see a little '' for the extras and if you click that you will see the edit option but you will also see all the list of the tools that you rarely use. You can't delete them forever (which is a pity).
Before you cancel or click done, there are some other features on the panel and they may or may not be useful for you. You can hold down the ALT key to reset all the changes made during the panel open so if you make a mess of the changes then you can just hold down the alt to get the reset feature instead of cancel. You can click cancel, of course, and leave and restart anyway. You can also click the restore defaults and that will just set everything back to the standard PS setup and that is fine also. You can click the clear feature which is useful as it dumps everything into the extra section and then you can drag the one or two items back to the main section on the left and use those. You can also click the save preset option which saves the settings all to a TBR format which is located in the presets section 'custom toolbars'. You can click the load option to bring in a particular set. If you are just painting or using the clone or dodge etc tools then you can set up one of the presets for those or perhaps you might want a set for the 3D features you can load those quickly and use those and replace them quickly with your main TBR setup. At the bottom of the panel you will see '' which removes the extra button so you won't see those less used items at all such as note tool or measure tool etc (I am certain everyone does use them but I can't think of many occasions for myself). The others are remove the foreground and background color though I am not sure why you would want to remove them (I use that all the time) as well as show quick mask mode and screen mode. There is also a final option to remove the extra's shortcuts which may or may not have any uses as I would assume if you don't use them that much you may have already removed those or used the shortcuts with something else.
This is a really useful addition and one I used from day one. I always use the custom shapes and having that feature at the top of my kit is really useful as I now no longer have to click to the bottom of the list of rectangle, rounded rectangle (does anyone use that now ?) and so on. I would love to see it extended further so the panel can be extended to four columns etc or perhaps dragging other features onto the panel such as the custom shapes presets so I can have them all in one place. Or perhaps finally opening the panel to third party tools as in Illustrator ?? Certain there are many more things to explore with this new CC feature. You can also go for a very very small set of features but why would you want that (as below). I would love to see 10s of new tools in the box (as in Affinity Photo)