Okay, a few tips:
- preorder your tickets, so you don't have to wait in the big crowd outside; you also save a few bucks this way. Last year I didn't have to wait in a line to enter the building at all: I just showed my printed out ticket, got a different ticket compatible to the card reader and could go right in.
- The preorder tickets are quite cheap (IMHO), only €8 for a student or €13.50 otherwise, here is the price list: http://www.gamescom-cologne.com/gamescom/trade-fair/ticket_2/index.php
- If you don't preorder, you pay €10.00 as a student or €16.00... if you are lucky to even get in (they don't sell additional tickets if it is too crowded)
- You can preorder the tickets here: https://tickets.koelnmesse.de/cipp/fmkm_visit/custom/pub/content,oid,4578/lang,2/ticket,g_u_e_s_t/~/Edit_your_personal_data.html
- the 2016-preorder tickets are personalized, so you can't give them away / sell them... probably to avoid scalpers this year
- Do yourself a favor and go on Thursday (and/or Friday), it gets more and more crowded every following day. Saturday is already sold out.
- Before entering the exhibition hall you can drink and eat outside for normal prices. There are enough options (it is right in the city). But if you want to eat or drink something while inside: don't worry, the prices inside are still okay. At some less popular stands they even offer you water or soft drinks for free (happened to me, when I tried out the iPad-DeusEx-game in 2013 or some Point&Click-adventures last year)
- Most short demo experience aren't worth waiting several hours in a line... so try to keep the number of games you really, really have to try out very small. There is enough to see in all these halls and the outside area without standing in line. Nowadays most AAA titles get an open beta anyways before they launch, which you can experience more comfortably at home.