Does Inflation Make Money Eventually Worthless? I used this calculator: http://www.buyupside.com/calculators/inflationjan08.htm
to estimate the future worth of 100 dollars in 100 years at 2% inflation. Does this really mean that a decent meal at a restaurant will cost about a $100 in the future or am I misunderstanding something? So basically what I'm asking is if at some point in the future will McDonald's Dollar menu become the Hundred Dollar menu?
"Worth less" than before - yes, that's exactly what inflation does.

"Worthless" - not quite. No percentage-based reduction in value can make something worth 0, but there are extreme examples from history of times inflation has spiralled so far out of control ("hyperinflation"), money became worth less than the paper it was printed on, and life savings became almost worthless. 

1920s Germany is the most famous example, but there are more recent examples, such as Zimbabwe. 

This is a real Zimbabwean banknote from 2009 - you don't need the terrifying inflation rates to see that savings of thousands of Zimbabwean dollars made in the early 2000s had become effectively worthless:



But those are extreme examples.



As for the idea of a McDonald's $100 Menu - it wouldn't be unbelievable looking at history. 

According to measuringworth.com, $1 one hundred years ago would buy the equivalent of $24 of common retail goods and the equivalent of $99 of the time of an unskilled labourer. A time-traveller from 1914 would expect a "$1 menu" to be high quality dining, worth days' wages for the average Joe. Not so different to how the idea of a $100 menu seems to us today,

This seems like a big change - but even this is a small change by international standards. 

The US dollar has historically been one of the world's most stable currencies, partly related to its use in international trading and its status as a reserve currency. In other countries, even countries with relatively stable economies, such changes do happen in a person's lifetime. Here in the UK, it's a cliche for elderly people to complain that "in our day", meals could be bought for sums of money that today would considered small change.



But even though it'd be perfectly believable, it might not happen. Beware of extrapolations that assume trends won't change (cartoon from XKCD): 



Anything could change. The US dollar might not keep its current world status. Governments influence inflation, and may sometimes simply change currency values if they feel it's getting out of hand. For example, in 2005 Romania knocked 4 zeros off its currency. 10,000RON became 1RON overnight.