The current version of Helpful Tweaks has this running inside it:
When run on a server and a client it will detect loaded inventories near players and then send an update to render overlays over filled inventories, Orange boxes are for inventories that have all slots filled but can still have items put into them. Red boxes mean that the inventory is completely filled to the brim.
This will not work with things that do not have inventories not directly tied to real-world objects, like enderchests.
second, if this is installed on a client only, a speedometer can be seen on the top middle of the screen, this will tell you how fast you are moving in blocks/second or m/s (they're both the same measurement) This works on a 3D scale and will tell you how fast you are falling to your death, swimming across a waterfall or just jumping over some particularly annoying blocks.
As for the config file, this is where you can put the names of inventories you do not want to be checked for filled inventories.