It would be nice if all the students showed up exactly on time - but... you know! I have a few ideas for "things to do while waiting for everyone to come", and I'd really like some more. The idea is to do something worthwhile (so the students who come on time feel they are gaining something), but not critical to the lesson (so people who are 10 minutes late won't be completely excluded).
This is for adults in an ESL environment, naturally what works for me won't work for everyone!
1. Hangman - Vocab to tie into the lesson, good stuff!
2. Battleships - As above
3. Horoscopes - Get horoscopes from newspaper or internet and then students in pairs, discussing what they mean.
4. Have a chat - Chat with students, keeping a piece of paper and a pen close by. Quietly record any mistakes / issues for improvement, then later put them all up on the board (but not saying who said what).
5. Review what we did yesterday
6. The memory game - "Yesterday I bought an apple", "Yesterday I bought an apple and a TV", "Yesterday I bought an apple, a TV and a guitar", etc...
7. Going over homework
8. Drawing games - Like, teacher shows student a word, student must draw it on the board, other student(s) guess what it is. Can be changed to orally describing instead of drawing. Nice to choose things which will be mildly relevant to the lesson.
9. Another one, students draw cartoons of what they did/were doing yesterday, swap around, others guess what it was.
10. Bingo - Assuming you have resource books with bingo in them! Good for pronunciation, minimal pairs, etc... There's an online bingo card generator somewhere...
11. Phonemic script - Translation stuff, what's the difference between /liv/ and /li:v/), write your name phonetically, can focus on specific student's pronunciation issues.
12. Just teach something - It figures that the on-time students are the keen ones. Sometimes they like it if you give them an extra "mini-lesson", or explain an obscure language point. For example, why don't we say "An university" - (because of the "y" sound when speaking), etc...
13. News review - (We have a free English language newspaper, but for those that don't maybe news printed from the internet?) - In pairs, choose an article, read so they can explain to class what it's about.
14. News headlines - Newspaper headlines aren't usually grammatically correct, get students to add articles, verb "to be" etc... to headlines.
15. Ask students - Ask if there is anything they would like to know about specifically, it's a nice "reward" for coming on time to get more personal time with the teacher.
I'm sure there are more, but that's all I can think of for now. Any more suggestions?

Leeroy