I've compiled a list of the top Spark accessories for April 2019. These accessories were chosen based on their sales volume on Amazon over the past month. If you're looking for some new accessories to add to your kit, this list will give you an idea of what other Spark owners are buying and using.
SKYREAT Foldable Tablet/Phone Mount
Notable features:

DJI Spark Battery
Notable features:

Threeking Parabolic Signal Booster
Notable features:

UZOPI Foldable Tablet/Phone Mount
Notable features:

DJI Spark Props
Notable features:

DACCKIT Carrying Case
Notable features:

Kuuqa Accessories Kit
Notable features:

DJI Spark Prop Guard
Notable features:

SKYREAT Foldable Tablet/Phone Mount (New Design)
Notable features:

Deyard Carrying Case
Notable features:

LEOBRO Accessory Kit
Notable features:

PGYTECH Tablet/Phone Mount
Notable features:

Fstop Labs Foldable Tablet Mount
Notable features:

DJI Portable Charging Station
Notable features:

SKYREAT Extended Tablet/Phone Mount
Notable features:

RC GearPro Battery Charging Hub
Notable features:
More details can be found here on Amazon.

HeiyRC Accessory Kit
Notable features:

Yx Parallel Battery Charger
Notable features:

Want to check out more Spark accessories? A commonly used list of Spark accessories sorted by category is available at Spark-Help.com.
SKYREAT Foldable Tablet/Phone Mount
Notable features:
- Made of aviation aluminum-alloy
- Able hold a mobile device between the width of 4-12 inches
- Mount can be swiveled sideways to hold a phone
- Hole at base to attach a lanyard
DJI Spark Battery
Notable features:
- Created, designed, and extensively tested by DJI
- Guaranteed to work well with your Spark since the battery is an OEM DJI accessory
Threeking Parabolic Signal Booster
Notable features:
- Boosts the remote controller signal to increase its range
- Folds closed for storage
UZOPI Foldable Tablet/Phone Mount
Notable features:
- Made of aviation aluminum-alloy
- Able hold a mobile device between the width of 4-12 inches
- Mount can be swiveled sideways to hold a phone
- Hole at base to attach the included lanyard
DJI Spark Props
Notable features:
- Created, designed, and extensively tested by DJI
- Guaranteed to work well with your Spark since the props are an OEM DJI accessory
DACCKIT Carrying Case
Notable features:
- Tough and durable hard outer shell
- Carry with the adjustable shoulder strap or side carry handle
- Can hold the Spark, remote controller, 5 batteries, charger, charging hub, and other small accessories
Kuuqa Accessories Kit
Notable features:
- Protect the remote controller sticks while in storage with the remote controller stick protector
- Lock the gimbal in place and protect the camera with the gimbal lock and cover
- Protect the props when in flight with the prop guard
- Shield the camera from the sun and protect the camera with the lens hood
- Protect your fingers when hand catching with the finger guard
DJI Spark Prop Guard
Notable features:
- Prevent the props from making contact with people or objects mid-flight
- Created, designed, and extensively tested by DJI
- Guaranteed to work well with your Spark since the prop guard is an OEM DJI accessory
SKYREAT Foldable Tablet/Phone Mount (New Design)
Notable features:
- Made of aviation aluminum-alloy
- Able hold a mobile device between the width of 4-12 inches
- Mount can be swiveled sideways to hold a phone
- Hole at base to attach the included lanyard
- This upgraded version is more durable since the plastic tightening ring has been replace with a metal ring
- Store the mount and lanyard in the included storage bag
Deyard Carrying Case
Notable features:
- Portable and lightweight
- Hard outer shell to protect the contents
- Can hold the Spark, remote controller, 3 batteries, charger, and other small accessories
LEOBRO Accessory Kit
Notable features:
- Lock the gimbal in place and protect the camera with the gimbal lock and cover
- Protect the remote controller sticks while in storage with the remote controller stick protector
PGYTECH Tablet/Phone Mount
Notable features:
- Able hold a mobile device between the width of 4-10.5 inches
- Mount can be swiveled sideways to hold a phone
- Swivels on a ball joint to adjust the angle of the mobile device
- Quick-release thumb screw allows you to attach and remove the mount quickly
Fstop Labs Foldable Tablet Mount
Notable features:
- Made of high impact ABS plastic
- Attach and detach within seconds
- Able hold a mobile device between the width of 4-12 inches
- 360 ball joint allows the tablet to be adjusted for better visibility
- Folds into a compact form factor for storage
- Hole at base to attach the included lanyard
DJI Portable Charging Station
Notable features:
- Recharge your Spark batteries out in the field with this 5000 mAh rechargeable battery station
- Charges up to three Spark batteries in 2.5 hours
- Recharge the charging station in 1.5 hours
SKYREAT Extended Tablet/Phone Mount
Notable features:
- Able hold a mobile device between the width of 4-12 inches
- Mount can be swiveled sideways to hold a phone
- Adjustable height and position
RC GearPro Battery Charging Hub
Notable features:
More details can be found here on Amazon.
HeiyRC Accessory Kit
Notable features:
- Protect the remote controller sticks while in storage with the remote controller stick protector
- Lock the gimbal in place and protect the camera with the gimbal lock and cover
- Prop mount bracket holds the props in place and protects them while in storage
Yx Parallel Battery Charger
Notable features:
- Charges 4 batteries simultaneously in about 60 minutes
- Able to also charge 2 USB devices
Want to check out more Spark accessories? A commonly used list of Spark accessories sorted by category is available at Spark-Help.com.