I spend a lot of time thinking about how I should spend my limited time on this planet. What human pursuits are meaningful and which are pointless? Should I be ‘wasting time’ playing the guitar? Should I be ‘wasting time’ going up a snow-covered hill only to slide down it? Is there some point to these pursuits or are we just tickling our neuroreceptors while we wait to die? What is the point of civilisation, anyway?
I find the answers most people give to these questions deeply unsatisfying. “Do you enjoy it?” The question of how much dopamine my brain releases doesn’t seem to be a good way of evaluating whether something is worth doing; to the contrary, there may be things that are worth doing that take a lot of effort and have delayed reward. “Are you making the world a better place?” Define better?
In order to arrive at a coherent argument for what is meaningful and what is not, it seems necessary to find grounding in terms of some deeper meaning or purpose in the universe. Unfortunately, it also seems impossible to find such meaning. Deconstruction of the universe through the tools of science leads one to arrive at the point where the universe is simply a bag of information and rules. While we can refine our knowledge of the information and rules, there is nothing further we can determine beyond that point — by definition, the universe is the closed system of things we can observe and measure. In particular we cannot determine the ‘reason’ or ‘purpose’ for the information or rules. If the universe is embedded in some higher space, we cannot determine that, and even if we could, the same arguably would apply recursively.
Camus called this the Absurd; to quote Wikipedia
, “the conflict between (a) the human tendency to seek inherent value and meaning in life and (b) the human inability to find any”. 
Even the Old Testament book of Ecclesiastes reflects on this theme. “I have seen everything that is done under the sun, and behold, all is vanity and a striving after wind.” … “Man cannot find out the work that is done under the sun. However much man may toil in seeking, he will not find it out. Even though a wise man claims to know, he cannot find it out.” 
So having pulled apart the universe into its gears and pulleys and failed to find the meaning we are seeking, there seems to be a number of directions we can take.
Like Camus I would discount the option of suicide. If there is indeed no meaning to the universe then suicide also has no meaning and no benefit, we are simply rearranging an alive organism into a dead organism. If there is a small chance that there is meaning to be discovered, then suicide precludes its discovery. Therefore in this context suicide seems to be all downside and no upside.
Secondly we could introduce God. I do not object to the introduction of such an entity, but I reject the claim that one can determine anything about God and what purpose that might introduce into our lives. Even the author of Ecclesiastes alludes to this in the quote above. Certainly we can use texts like the Bible as philosophical food for thought but they are fundamentally works of humankind and are limited by the same limitations of insight that apply to all of us. So we are still left to choose our own philosophical path out of the remaining options.
Next we could assert, without proof, that human emotions have intrinsic meaning, and therefore the goal should be to increase well-being and decrease suffering. But we know that emotions are simply chemical phenomena, and we often use our emotions or perceived emotions to manipulate other people, so I find this option unsatisfying.
Fourthly, we could take the option offered by the author of Ecclesiastes: accept the lot that we have been given, and enjoy the little things in life. The problem is that we do need to make decisions in life, and without a clear philosophical framework it is difficult to decide whether we should help starving children or keep playing Tetris.
There is yet a fifth path that I would suggest is more defensible than the others. Let us accept that the measurable universe may be nothing more than a bag of information and rules. But this is merely the fabric out of which the universe is woven. Out of this fabric emerge patterns and structures. Not just simple structures like lattices, but self-aware structures like the human mind, and incredibly complex structures that inspire even the human mind with awe and wonder.
I think Camus is right that a key word is ‘beauty’: a word that we use to describe structures that possess a certain sort of complexity. The religious person will attribute this beauty to God, the atheist to Nature, I would say they are one and the same, but in any case I think this concept of beauty is at the core of how we can find meaning in a universe that would otherwise seem meaningless.
As a result I would propose that there are at least four things that can usefully provide meaning for human beings:
- Discovering beauty (science)
- Creating beauty (art)
- Protecting beauty (conservation)
- Nurturing other human beings to experience beauty (love, connection, teaching, medicine, etc.)
This is not yet a complete ethical system, but I feel like it’s an important step in establishing a philosophical viewpoint that can be defended from the bottom up, while avoiding the void that comes from taking reductionism to its very end.
(Sadly sliding down snow-covered hills doesn’t really make the cut in this list. But we can also allow ourselves a bit of fun sometimes. Or maybe even a lot of the time. There’s some beauty in reckless abandon.)
 Apologies for quoting Wikipedia rather than Camus, but I think it is very well put. Camus wrote: “At this point of his effort man stands face to face with the irrational. He feels within him his longing for happiness and for reason. The absurd is born of this confrontation between the human need and the unreasonable silence of the world.” (The Absurd Man)
 Ecclesiastes 1:14, 8:17 (ESV)