A Pointless Endeavor

Question

I found an box of weird junk in my Grandmother's storage closet earlier this week. It included:

• A tin can, painted green
• Another can, this one an old store-brand Diet Root Beer can in light brown
• A burned CD-ROM: orange marker indicates it contains a copy of Second Life
• In a tiny baggie, a pink pill that I think is MDMA
• A light blue gram weight from one of those calibration sets

There was a sixth item in there, a tiny bottle, but I fumbled it and it fell into a dark corner with the sound of shattering glass before I could get a good look at it.

Honestly, I was ready to throw the whole box out (my grandmother doesn't even have a PC with a CD-ROM drive, and the less thought about the club drug the better), but when I mentioned it to my grandmother, she said that it was a "silly little collection" of hers. Now I feel sort of bad that my clumsiness broke up the collection. I'd like to replace the last object, but I'd really like to not mention that I broke something of my grandmother's before I have the replacement in hand. So...

What do I need to complete the collection?

Answer 1

Perhaps the last bottle was

A yellow bottle containing hydrogen

Reasoning

Your grandmother likes to collect things which have colours and initials corresponding to the categories in Trivial Pursuit

A green tin can
Tin has the chemical symbol Sn and the green category in Trivial Pursuit is Science and Nature.

Another can, this one an old store-brand Diet Root Beer can in light brown
I think this refers to A&W diet root beer. The brown category in Trivial Pursuit is Arts & Writing (Arts & Literature).

A burned CD-ROM: orange marker indicates it contains a copy of Second Life.
Presumably the CD would be marked SL and the orange category in Trivial Pursuit is Sport and Leisure.

In a tiny baggie, a pink pill that I think is MDMA
MDMA is also known as ectasy or e and the pink category in Trivial Pursuit is Entertainment.

A light blue gram weight from one of those calibration sets.
Presumably, this would just have g written on it and the light blue category in Trivial Pursuit is Geography.

The final category is the yellow History category so your grandmother would need something yellow with a H on it (hydrogen works but it could also be heroin).

Title

"Pointless Endeavour" is a synonym for "Trivial Pursuit"