Any issue with lights is easily solved with a sleeping mask. That said, all you have to do is stay calm for a few hours, so the best think you can do to improve your travel is stop imagining that it will be a nightmare. If you are so convinced that your travel will be an ordeal ("surviving"), then you most probably will have a bad experience even if everything is ok.

@pnuts You should write that as an answer

In addition of the answers, some countries allow you to buy the visa at the arrival (e.g. airport), making it more of a tax that a real control measure. For example, until relatively recently Turkey used that system.

@HenningMakholm That is discrimination, **but** nations are allowed to do it**...**. If o.m. had said that in the meaning you explain, the but would have been not necessary. Additionally, he had already said that the treatment was based in nationality so it was discriminatory (in the sense you use), so he would have been repeating himself needlessly (as in "this towel is soaked in water, and is wet"). o.m. used that term to mean that it was an unethical or inmoral criteria.

Additionally, for many of the major and most used beaches there are crews that clean and pick up trash in the morning. If you leave your belongings in the area they have to clean that day, they will do their job and clean their area.

In Spain, effects left overnight are usually retired. You do not own a spot in a public place, preventing someone else using it by placing a towel is an uncivical actitude. To measure these things it is usually worth thinking what would happen if everybody did the same thing, or if someone took a prime spot in June 1st and did not remove the towel from there until Setember. Or someone who leaves the towel and appears two day later. If you value this or that spot so much, make the effort of getting up earlier to be in there sooner than other people.