I'm thinking of joining (it's my senior year). I'm only in marching band, and I can read music well enough for clarinet and much better for piano. However, I only know first position notes on the guitar, and I play the rest by tabs.

Will it be necessary for me to know the notes all the way up the fretboard (yes, I know there's a pattern), or does the guitar music come with both standard and tab notation? If it's just regular notation, I'll probably just play keyboard...

I'm not a Bible-thumper anymore. Realized I had a brain in '09.

I like guitars, running, and math.
The best you'll get with a swing chart is a chord chart that has the chords in the arrangement written out in tab. You'll need to know where the notes are on the guitar in relation to the notes that are above the ledger lines which will be out of treble clef.
12 fret fury
You could always tab it out yourself if you can't read fast enough to play it without. Work it out slow time, write it out in tab, then you have something to use for band practices and you'll have learnt more in the process.
in my experience, all big band guitar charts alternate between chords and for melodies standard notaton. but mostly chords, especially for older stuff, if there is a melody you have its usually a unison line with someone else, or at least rhythmicaly co-ordinated with another section. almost all the notes you'll be playing (melodically) are confortable in 2nd position (not very hard to learn if you know open), fifth position (not bad to work out if you know second) or 12th (same as open). As you learn the notes all the way up the fretboard, it becomes easier to learn more of them (go higher up). But you'll mostly be reading chord charts. If you want to play with other musicians you really should be fluent with standard notation though.
There won't be tabs. It'll be chords (notated as the chord names above slashes for rhythms), and then melodies (in standard notation). The melodies don't usually go too high, so what you are already comfortable with, should be close to enough for now. You should give it a try, and you will definitely improve.
Thank you. The band director asked me one day at marching band if I were going to play, and I hadn't even thought about it. I said maybe for piano because that's what I'm more comfortable with (musically speaking, theory wise too) but practice doesn't start until November, so I'll make it a point to practice reading, learning second and 5th position, and chords.

Again, thanks
I'm not a Bible-thumper anymore. Realized I had a brain in '09.

I like guitars, running, and math.