Supplemental Packs (1966-1968)
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Samsonite's original line of Supplemental Packs (1961-1965) was formatted similar to every other market for LEGO in the world. As covered in the linked article, however, there were 140+ different supplemental packs and sales of certain packs/colors lagged severely, so much so they were overproduced by Samsonite.
And so, after having completely redesigned their LEGO basic sets in 1965, Samsonite redesigned their supplements line in the following season.

"LEGO announces a completely new extra parts program with packages that provide wonderful eye appeal through the use of clear film wrap. The number of boxes in the extra parts line has been reduced from 144 to 14, including only the most popular assortments."
Supplements were now called "Extra Parts":
Prices for these were different, previously most supplements were 50c. Now, they ranged from $1-$1.50:

Sets from 1966-68 are easy to identify, as they are simple cubes with a small paper insert to differentiate each set.
As can be seen between the two above sets, there were some inserts in blue and others in white. This was to differentiate pricing between supplements that cost $1 and ones that cost $1.50.
Also, comparing the above and below 055's, the formatting of certain elements varied:
In addition to the basic part assortments offered (see above scans for more details), there were also a range of baseplates offered in different colors: green, white, and blue. They would come with a paper insert and be sealed in a stack:

I fortunately own all the paper inserts loose and have scanned them:



These supplements are much easier to collect compared to the earlier sets, though complete examples are much harder to come by due to the loose paper insert. For example, owners of the above baseplate supplements rarely kept the paper, so most collectors would have to source sealed examples.
A shipping box for these happens to have survived, it can be viewed at the History Colorado Center in Denver.
This box dates to somewhere between 1967-68, as that was when the Loveland brand name was in use by Samsonite on sets such as the LoveLand Dubl-Fun Block Wagon. It was replaced in 1969 in favor of just the Samsonite name.
Also, do note that categorically, Samsonite treated the 799 Baseplate as a supplement, that is covered in its own article.