Yo, read this very carefully:
Get a lawyer.
This is what's going to happen. Your possession charge is going to cost you about $1,000. Maybe a little more. The only question is, do you give that $1,000 to a lawyer and walk away with no record and no community service, or do you give it to the court and your probation officer.
I have been in this situation before. If you don't get a lawyer, you are going to get a public defender. If you get a public defender, the judge is going to slap you with a $250-$500 fine, then you're going to pay $50 a month to a probation officer for a year. Maybe more if they make you take alcohol abuse classes.
But, you go get a lawyer, the man makes it go away. That's what they do with this petty shit. The lawyer is buds with the prosecutors and the judges. Your case will be over before it even begins. You'll walk in, get a PBJ, and walk out. If you're lucky, you won't even have it put on your record.
Get a lawyer. I cannot emphasize that enough.
Problem is lawyer costs 
Dude, your fines are going to cost too. And in answer to your question earlier, you pay fines
immediately, as in the day of trial. They will let you leave the court to hit an ATM or whatever, but the court isn't about to give you a payment plan.
A lawyer, which DOES cost, at least can be negotiated with, and paid in installments.
Bottom line: you are paying either way.
Little personal anecdote: When I was in college, around 20, I was arrested for possession of alcohol and for drinking in public. I was having a beer in someone's front yard. I went with the public defender. Got slapped with 2x $250 fines, $50 a month in probation costs for a year, and had the convictions placed on my personal record.
Fast forward to last year. I had an interview for a job. Did very well, was told I had the job, but had to submit to drug and background testing. Passed the drug test,
failed the background check because of the open container and underage possession convictions. This is
7 fucking years later, and that shit is still kicking around my personal record, fucking with my life. Now, thankfully, my future (or I guess current) boss went to bat for me, and got corporate to make an exception. But if he hadn't, I would have missed out on a great oppurtunity because of some silly shit almost a decade ago.
I am going to get those charges expunged as soon as I can. This will probably cost me many hundreds of dollars, but it will be worth it.
Anyway, that's my story, and that's where I'm coming from. A lawyer has a very good chance of getting you out of court with no convictions and no fines. A public defender has basically no chance. You pay now either way, and if you get slapped with fines and a conviction, you pay later.