Portable repeater ideas.
Here are examples of various commercial and amateur portable repeaters to spark your imagination.

SPECIFICATIONS OF THE PTR-200 PORTABLE TACTICAL REPEATER

UHF FREQUENCY RANGE: 403-475 MHZ.
VHF FREQUENCY RANGE: 134-174 MHZ.
114 channels for each radio
8 character alpha-numeric display
Field programmable without a computer
RF variable from 10-40 watts UHF, 15-50 watts VHF
Redundant UHF receiver or transmitter
May operate as a UHF repeater or UHF link with a VHF link or may be used as two independent UHF radios and an independent VHF radio
Local switch for cross-band/tri-band repeat (Master radio, Auxiliary-A, Auxiliary-B)
Remote activation/deactivation via DTMF signaling from any or all three of the radios
Local supervisory switch overrides remote activation or de-activation
Programmable courtesy beep alerts receiving side that the other party that the channel is available
Low voltage sense input and programmable alert beeps for emergency battery back-up applications
Programmable station ID (up to 10 characters)
All controller programming can be accomplished via DTMF signaling from any of the radios
Water Resistant Roto-Molded case
UHF Repeat mode does not require duplexer in "10 watt RF mode"
Field operating manual provides instruction in using vertical separation vs. duplexer
Optional duplexer is available for single antenna deployment
Full PTR-200 system includes UHF & VHF antennas, masts, guy lines, low-loss coaxial cable, 100 amp lead acid battery, internal eight hour lead acid batteries, 20 amp metered power supply/battery charger, accessory case & 24/7 customer support.
Dimensions & Weight: 19"W x 19.5"D x 10"H 50 lbs. with internal batteries installed

Nida Communications portable repeater duplexer

PTR-DK/633-6A-2N
Nida Companies Tactical Repeater Duplexer Kit, which includes the following: 
    Waterproof International Orange color container 
    Celwave 633-6A-2N UHF mobile duplexer, tuned to specifications 
    Internal wiring harness with sealed bulkhead connectors to ensure watertightness 
    Two 3' RG-214 jumpers with male "N" Connector

Team One Communications built two of these 100 watt portable UHF repeaters for the city of Hialeah Florida.

Baker to Vegas Race uses portable UHF repeaters.  Click here to see photos of their radio equipment.

KQ6XA portable simplex "repeater" in a box.