All apps available on the Apple App Store for free or very cheap:

Tonal Energy Metronome - The best metronome and tuner combination app with so many options for customization.

IMSLP - Free public domain music app and website. The app allows for a convenient place to store the scores you find on the website as well.

forScore - For tablet users, this is by far the best sheet music reader out there. There are many options for organizing and tagging your scores.

GarageBand - If you have students interested in producing songs, this is a great app to have for them if they have iPads. They will be able to sing into the app, connect MIDI devices and play things into the app, and use a variety of different sounds and effects.

Voice Memos - Great app for quick audio recordings of practice sessions, performances, and rehearsals for later analysis.

Pulse - Pulse is a basic metronome that is free on the app store (very simple!)

Fingerings (orange logo) - A great app with different instrument fingerings. You select the note on the staff and it shows a fingering directly to the left of the staff.

Andante - Free app to log practice sessions for instruments with the option to record your session, track mood/focus levels, add notes to each practice session, and keep a running journal of your progress on your instrument. Also includes a "streak" feature similar to Snapchat.

Adobe Scan - Free scanning app to scan documents (Built-in Files app can do the same function but sometimes looks worse and has fewer document editing features). It is easy to export straight to ForScore once you edit the document in Adobe Scan. I highly suggest cropping in the app, adding the grayscale filter, and turning the contrast up to 100%.

Chet Ear Training App - Still testing this out but it looks like a great option to help improve your aural skills or to help your percussion section easily identify intervals they need to tune for their timpani parts.

Reverb - There are so many good instrument deals here to keep a look out for!

Haptik Apple Watch/iPhone simple metronome - The free version allows you to use your Apple Watch to tap a tempo and then will vibrate both your watch and iPhone to the beat. I have commonly used this at indoor percussion competitions to get tempo before counting my students off.

Google App Suite - In general, all Google apps have served me well. I currently use it to host things related to private lessons, a spreadsheet that holds all of the instrument gear that I currently own, tax documents, compositions, and other school-related things.
Tempbox - Mac app that allows you to generate temporarily email addresses for sites that unnecessarily collect your personal email address and involuntarily sign it up for a mailing list.

Keyboard Mallets: 

Salyers Percussion Earth Tone 90/100s - Great set of hemp-woven mallets for both marimba and vibraphone. I mostly use them on vibraphone but while I am teaching they are a great versatile option for demonstrating without pulling various pairs of mallets out of my bag.

Malletech: I use these models of Malletech mallets at least once a week whether I am teaching, playing in a small percussion ensemble, or playing in a large wind ensemble environment.

Malletech Concerto Series: I use both the CN14 and CN21 models. Very warm at low dynamic levels while still having bite at higher dynamic levels.
Late Nite LN1's - Great mallets to use late at night and into the morning, barely anything besides the contact sound is heard from the room over.

Malletech BB32 - Soft and hard - two toned.

Malletech BB34  - Medium hard - medium bright mallet. The "Becker Blues" are my go-to mallets for any xylophone work. 

Malletech NR13R - Rubber, medium.

Malletech NR19R - Rubber, medium hard.

Malletech ORMG36 - "A beautiful mallet for single-note passages like Sleeping Beauty." Enough articulation for rhythmic clarity, but warm enough to sound pleasant. My go to mallet for glockenspiel!

MalletechORBB - Small brass bead mallet, very bright. Works great on crotales and glockenspiel!

Timpani Mallets:

JGPercussion CL2 "Bartok" - Go to mallets for anything that needs articulation with some warmth.

JGPercussion CL6 "Sibelius" - Go to mallets for large sustained rolls.

Other sticks:

Cooperman

Promark Concert One - Large concert stick.

Promark Firegrain 5A with acorn tip - Generic 5A with a wood texture.

Brushes - Vic Firth Heritage Brushes (wire), Promark Light Nylon Brush 5B (plastic)
Instruments:

Black Swamp Tambourine TC2S with synthetic head - Great sounding tambourine, thumb rolls sound amazing!

Marimba One Educational 5.0 Marimba - This 5.0 padauk practice marimba features an easy to use height-adjustment system that one person can use. It comes with a dust cover and a pair of Round Sound mallets included. If you need a practice instrument that doesn't sacrifice on bar size and has a high quality frame, this instrument is for you. (Resonators not included and not available for purchase on the 5.0 model)